The Elements of 
PHysiologV 




WALTERS 



PUBLISHED BY 
E. W. STEPHENS, COLUMBIA, MISSOURI 




Class J^iJii^ 
Book -W z 2 r 
Gop>TightT\ TO 

COPYRIGHT DEPOSIT. 



THE 



ELEMENTS OF PHYSIOLOGY 



BY 



FRANCIS M. WALTERS, A. M. 



INSTRUCTOR IN STATE NORMAL SCHOOL, 
WARRENSBURG, MISSOURI. 



PUBLISHED BY 

E. W. STEPHENS, COLUMBIA, MISSOURI, 

1902. 



THE LIBRARY OF 

CONGRESS, 
Two Co*i-.c Recswed 

27 1902 

CLASS ^-^XXa No. 



H-1~ ^ 



B. 



COPYRIGHT.. 1902, 

BY 

FRANCIS M. WALTERS. 



The new physiology differs from the old 
in the determination of the functions of 
organs from the inherent properties of their 
protoplasm, in the study of these functions 
in a great variety of animal types, especially 
of the lower forms, and in the frequent re- 
course to physical and chemical laws for ex- 
planations of phenomena. — LoeVs Lectures 
on General Physiology. 

\Jtt \6 tit* 

"It is quite possible to give instruction 
in this subject (physiology) in such a man- 
ner as not only to confer knowledge which 
is useful for itself, but to serve the purpose 
of a training in accurate observation, and in 
the methods of reasoning of physical 
science." — Huxley. 




Fig. i. The Physiological Scheme^ See Summary of 
Part I, page 92, and Summary of Part II, page 176. 



PREFACE. 

This small treatise on the human body differs from the usual 
school text-books on this subject in the emphasis which is placed upon 
physiology. Only enough anatomy is introduced to construe the gen- 
eral structure of the body, while the hygiene is limited to suggestions 
and deductions growing out of a knowledge of physiology. The view 
is maintained that "the great art of right living" consists in the har- 
monious adjustment of one's habits to the nature and plan of the body, 
Such adjustment can be successfully accomplished only to the extent 
that one has a comprehension of the life processes and of the nature 
and extent to which they are influenced by modifiable conditions. 

Another reason for placing the emphasis upon physiology is that 
by so doing the general purposes of education may be served as well as 
the practical purpose for which the body is studied. Physiology is a 
branch of natural science and, like biology, chemistry, or physics, may 
be so taught as to tax the reasoning powers, develop insight, and drill 
the pupil in the modus operandi of natural forces, 

Much of the usual discussion of stimulants and narcotics has 
been curtailed for the reason that an undue amount of time spent in 
their consideration detracts from the symmetry of the subject and 
gives a distorted view of their physiological importance, and for the 
further reason that the general phases of these topics are properly con- 
sidered in the lower grades. In confining this discussion to what seems 
to be its natural place in the pedagogical scheme, however, care has been 
taken to state accurately and pointedly the physiological objections to 
the use of alcohol, nicotine, and other poisonous drugs. 

In the arrangement of the different chapters that order has been 
selected which promised to give the pupil, at each successive step, a 
deeper insight into the plan of the body. Since the body is but a 



v PREFACE. . 

complex mechanism for the maintenance and transmission of life, the 
natural, or biological order, has seemed the one best adapted to this 
purpose. From the biological point of view the subject falls naturally 
into two divisions — the consideration, first, of the organs and the 
processes directly concerned in the maintenance of life and, second, 
of the mechanisms that co-ordinate the different parts of the body and 
bring it into proper relations with its environment. 

Observational work should be carried on to the extent, at least, 
of obtaining clear ideas of the parts considered and of the processes 
involved in their operation. Systematic laboratory work, where it 
can be arranged for, is a most valuable aid in the mastery of the sub- 
ject. Where this cannot be provided, class experiments and observa- 
tions must be supplied by the teacher. The experiments and observa- 
tions given in this book are for class purposes and are intended to 
serve a necessary part in the development of the subject. The list, 
which is suggestive rather than exhaustive, includes such as are simple 
and require little apparatus. A note book should be kept by the pupil. 

The habitual use of books of reference in the study of physi- 
ology is earnestly recommended. For this purpose the usual high 
school books may be employed to good advantage. A few of the more 
advanced text-books should, however, be frequently consulted. For this 
use Martin's Human Body, Advanced Course (Henry Holt & Co., 
~N. Y.), Rettger's Advanced Lessons in Physiology (Inland Pub- 
lishing Co., - Terre Haute, Ind.), Thornton's Human Physiology 
(Longmans, Green & Co., N. Y.), Huxley's Lessons in Elementary 
Physiology (The Macmillan Co., N. Y), An American Text-Book of 
Physiology (W. B. Sanborn & Co., Philadelphia), Potter's Quiz- 
Compend (P. Blackiston's Son & Co., Philadelphia), Kimmins' 
Chemistry of Life and Health (Methuen & Co., London), Egbert's 
Hygiene and Sanitation (Lea Brothers & Co., Philadelphia), and 
Florence Nightingale's Notes on Nursing (D. Appleton & Co., N. 
Y.) will be found quite serviceable. 

The subject matter of this book has been criticised by Dr. Thomas 
D. Wood, Physical Director, Teachers' College, Columbia Univer- 



PREFACE. ■ vii 

sity ; by Dr. J. I. Anderson, practicing physician at Warrensburg, 
Mo.; and by Prof. J. L. Ferguson, Instructor in Physiology, State 
Normal School, Warrensburg, Mo. Kev. Dr. R, Neale of Warrens- 
burg, and Mrs. Jennie E. Walters reviewed and criticised the literary 
features of the book, while the proof-sheets were kindly read by Profs. 
Deerwester, Seawell, and Ferguson of Warrensburg, and by Dr. C. 
C. Guthrie, Ass't Demonstrator, Medical Dep't, Western Reserve 
University. Dr. C. M. Jackson, Dep't Anatomy and Histology, Mo. 
State Univ., reviewed the portions on anatomy. 

The drawings for the zinc etchings were prepared by S. Fred 
Prince, biological artist, Lincoln, Neb. 

The general plan of the book, much of the subject matter, and 
most of the experiments and observations have been drawn from the 
author's Physiological Class-Book, publication of which is discon- 
tinued. 



TABLE OF CONTENTS. 



Part I. The Yital Peocesses. 

CHAPTER. PAGE. 

I. The General Construction and Work of the Body . 1 

II. The Blood 7 

III. Circulation of the Blood ..... 14 

IV. Lymph and the Lymphatics . .... 24 
V, Respiration 29 

VI. The Passage of Oxygen Through the Body . . 39 

VII. Foods . . . . . - . . .45 

VIII. The Abdomen and its Contents 53 

IX. Digestion .57 

X. Absorption, Storage, and Assimilation . . . 70 

XL Liberation of Energy in the Body .... 78 

XII. The Excretory Work of Glands " .... 83 

Summary of Part I ...... 92 

Part II. Motion, Co-ordination, Sensation. 

XIII. The Skeleton 93 

XIV. The Muscular System 101: 

XV. The Skin . 113 

XVI. Plan of the Nervous System 119 

XVII. Work of the Nervous System .... 128 

XVIII. Production of Sensations 141 

XIX. The Larynx andjthe Ear . . . 147 

XX. The Eye 157 

XXL The General Problem of Keeping Well . . 169 
Summary of Part II . . . . . .176 

Appendix 177 

Index 181 



THE ELEMENTS OF PHYSIOLOGY 



PART I. 



THE VITAL PROCESSES. 



CHAPTEE I. 

THE GENERAL CONSTRUCTION AND WORK OF THE BODY. 

Definitions. The study of the human body falls naturally into 
three divisions, known as physiology, anatomy, and hygiene. 

Physiology is the study of life processes and their interpretation, 
as far as is possible, in terms of known laws and facts. It may be gen- 
eral or special, according to whether it treats of life as manifested in a 
variety of animals or plants, or of the life processes in a single type. 
Human physiology is a special branch of the subject which deals with 
the function, or use, of the different parts of the body of man and of the 
relations they sustain to each other and to the body as a whole. 

Of vital importance in the study of physiology is a knowledge of 
anatomy. Anatomy treats of the construction of living bodies — the 
nature and location of their parts and the materials from which they 
are formed. It is of two kinds, known as gross anatomy and histology. 
Gross anatomy is the study of the. rough, coarse structures, while his- 
tology treats of the minute structures — those parts that are too small 
to be seen with the naked eye and which must be investigated with the 
aid of the microscope. 

The practical value of physiology as a subject of study, in our 
public schools, lies in its bearing upon the health. Methods of caring 
for the body that relate directly to the health are considered under the 
subject of hygiene, while the conditions that must be observed for this 
purpose are termed the a laws of health." Since these are all included 

1 



a SLEMEWl J OF J tY. 

in the general principle that right habits of living I : with the 

plan of the body, the value of a kn _ of both physi logy and 

anatomy from the standpoint of h _ : f arent 

Tissues. The body appears, from a hasty examination, 6c be a 
combination of several dissimilar substances tissues. Foi 

mining the relative i nature of the differ ent tissues, tfa 

of some small animal may be studied with profit. 

Observation. Examine with eare the different structures in the entire leg of 
a squirrel, rabbit,, chicken or other small animal. 0" r -: r fiisi 

:.:- . :;-t:::_ : : --:--;•:_ :: :\;:::'.t -r_* . •::. .:- -:..•'.:• :r :-:"::>. ::::.:". :: 
the specimen. These are similar in strueture, and form the epidermal 
With a sharp knife lay open the skin and observe tha - 

underneath by thin, but tough, threads and sheaths. They represent a variety 
of structures which connect different portions with each other and are called con- 
nective tissue. The muscular tissue, which may now be examined and w\ 
forms the greater portion of the animal, is easily distinguished by its reddish 
pearance. With a blunt instrument, separate the muscles, by tearing apart - 
>;"r:::--f :: — ' r ^'..- •-'_- :■.'! r_:\ i :Lt : :_": -:::;- :: ::n-T::i^r :: — Mr :' - "-i- 
dons) which attach the muscles to the bones. Find near the central part of the 
leg some white glistening cords (nerves) which form one varier - : 
-_ :he ends of the bones [osseous tissue) find a layer of smooth cartilaginous 
tissue. The adipose, or fatr~ tissue is found immediately beneath the skin and 

Kin :1s :: Tissues." In ;-_ ;".- -■; I. :\= :Le : ~~r. "It fal- 

lowing tissues -lould be found: 

1. Epidermal tissue (three varieti— i Connective tissue 
(fibrous varietie- Adipose n : tissue - Muscular tissue 

:~:ated variety sseous tissue: 6. '. _ as tissue 7. 

ssue (nerves 

These ssues form the greater portion of the body. Others less 
abundant, but of considerable importance are : 8. The nervous tiss 
of the brain and spinal cord. 9. Non-striate nsculai tissue 10. 
I; [-1 I \. :Ui"- 

Nature of the Tissues. The tissue- serve the 

body similar - I of wood, si : plaster, iron and other like m 
rials in a house. As the house is constructed from these building m 
rial- rj uilt out of the tissues. For this reason the - 

have been called : .lding materials of the body. But the tissn 



♦In the more recent works on : -eons, and earr 

--^d as varieties of eonne d sue, and the epiderm 

rariety of epithelial tissue. 



CONSTRUCTION AND WORK OF THE BODY. 



are also the means through which the work of the body is carried on,, 
and in this sense, sustain a relation to the body additional and superior 
to that of building materials. 

Properties and Uses of Tissues. Each tissue is found to serve 
some definite purpose in the body. It is also found to be perfectly 
adapted, by its properties, to its purpose. The properties of tissues 
like those of inanimate substances, are their distinguishing qualities, 
or characteristics, and may be either physical or chemical. With refer- 
ence to hardness, toughness, color, weight, elasticity, and other proper- 
ties, great variety is to be found among the different tissues. Further- 
more, while each tissue may, and usually does, possess properties of 
minor importance, it also has properties which are indispensable in 
adapting it to its place in the body. Some of the more important of 
these essential properties are as follows : 

1. Of osseous tissue, hardness, toughness and stiffness. 2. Of 
muscular tissue, contractility. 3. Of nervous tissue, irritability. 4. 
Of cartilaginous tissue, stiffness and elasticity. 5. Of connective 
tissue, toughness and pliability. 6. Of epidermal and epithelial 
tissues, toughness and resistance to the action of external agents. 

Composition of Tissues. All tissues are made up of two dis- 
tinct types of material. One of these consists of minute particles 
called cells; the other is a substance lying between the cells, known as 
intercellular material. The cells are, for the most part, too small to 

be seen with the naked eye, the 
largest not exceeding one two-hun- 
dredth of an inch in diameter. 
They are found to be unlike in the 
different tissues and to vary in form 
and properties to suit their places 
in the body. 

The intercellular material is 
generally produced and deposited by 
the cells. Its quantity varies with 
age and increases with advance of 
years. It differs both in quantity 
and quality in the various tissues, 
Fig. 2. varieties of animal ceils. i. and is the source of special physical 

Epithelial cells from the mouth. 2. Cartilage prop€r ties Slich as the StiffneSS of 
cells. 3. Pigment cells from the retina. 4. x x 

Liver cells. 5. Non-striated muscle cells. bone and the elasticity of cartilage. 




i ELEMENTS OF PHYSIOLOGY. 

Observations. 1. Mix some of the scrapings, made from the inside of the 
cheek with a dull knife, with a little water on a glass slide. Place a cover glass 
on the same and examine with a compound microscope. The large cells that may 
be seen in this way are a variety of epithelial cells. 

2. Mount in water on a glass slide some very thin slices of cartilage and 
examine first with a low and then with a high power. (Such slices may be 
cut with a sharp razor from the cartilage found at the end of a rib of a young 
animal.) Cartilage is remarkable for its intercellular material which forms 
a kind of bed for the cells. 

3. Also mount and examine with the microscope, thin slices of elder pith, 
potato., and stems of growing plants. Make drawings of the cells thus observed. 

Structure of the Cell. The cell is usually described as hav- 
ing three parts — the cell wall, the protoplasm, and the nucleus. 
The cell wall is a thin covering surrounding the other parts. It offers 
more or less protection to the cell contents, but since it is absent in 
, ^ — ^ many instances it is not regarded as essential to 

*"/"/$tis \ T " le ^ e °^ ^ e ce ^" ^ e P r °t°pl asm ^ s aJ l the 

3 "f \£J0 ] space within the cell wall and is the essential sub- 

a V J stance of the cell. It is semi-liquid and somewhat 

\^__^/ granular and resembles in appearance the white of 

Fig. 3. a typical a raw e gg- Living protoplasm is capable of slight 
Cytopiisi£ el 3. Nucleus; motion and responds to irritation. It can absorb 
4.' Attraction sphere. and appr0 p r i ate li qil id food. It is absolutely es- 

sential to the cell and has been called the "'physical basis of life." 
The nucleus appears as a clear rounded body within the protoplasm. 
It is concerned particularly with the formation of new cells and consists 
of a variety of protoplasm which is termed the nucleoplasm. Xear 
the nucleus a small body has been discovered, named the attraction 
sphere, and within this is a denser portion called the centrosome. 
These also play some part in the development of new cells. 

The entire cell is properly regarded as an organized bit of protoplasm, while 
the parts described above are but the modifications presented by it at different 
places. The cell contents, outside of the nucleus, is called the cytoplasm. 

Conditions Surrounding the Cells. The cells of the body 
are aquatic, that is, they are surrounded by liquids which are essential 
to their life and activity. These liquids supply the cells with oxygen 
and food substances and receive and dispose of their waste materials. 
They find their way through the channels and spaces in the intercel- 
lular material of the tissues, keeping the cells well supplied with mois- 
ture. The liquid coming in immediate contact with the cells is called 
the lymph. A second liquid, the blood, replenishes the lymph and 
receives the waste that passes through the lymph from the cells. 



CONSTRUCTION AND ^YORK OF THE BODY. 5 

Activities Of the Cells. Each cell is the center of certain ac- 
tivities which are referred to as the work of the cell and which are in 
part general and in part special in nature. The general work of cells 
includes those activities that are necessary for their maintenance in 
the tissues and which are common to all cells. These are the absorp- 
tion of liquid food and oxygen from the surrounding liquids, the pro- 
duction and addition of new material to the protoplasm, and the cast- 
ing out of waste materials, or excretion. The special work of cells 
refers to the particular form of service that a given class of cells may 
render to the body as a whole. For example, the special work of 
muscle cells is to bring about the different movements of the body, 
while that of gland cells is to secrete various liquids. 

Formation of new Cells. In all the tissues there occurs, 
at some stage in the growth of the body, the process of cell formation, 
or reproduction. In a few tissues, such as the epidermal, this process 
takes place continuously during life in order to supply new cells for 
replacing old and worn out ones. New cells are always formed from 
old ones. The most common plan by which this is accomplished is 
called cell division. By this plan a single cell after attaining its 
growth, separates into two or more new cells. The new cells thus 
formed begin at once to grow, absorbing liquid food and oxygen and 
may, upon attaining their full size, divide to form other new cells. 

Importance of Cells. The body may be regarded as a vast 
collection of cells, of as many varieties as there are tissues, which are 
mutually helpful to, and also dependent upon, each other. All the 
work of the body is accomplished through its cells. The body grows 
through their growth and reproduction, and is nourished and kept 
alive through the agencies that nourish and keep alive the cells. A 
knowledge of the structure, growth, and work of its cells, therefore, is 
the first step toward a clear understanding of the body. 

Organs and Systems. Any part of the body that has some 
special work to perform may be called an organ, as the eye, which is 
the organ of sight ; or the hand, the organ for grasping. Any given 
organ will be found to contain the tissues necessary for its work. In 
an organ, like the hand, most of the tissues of the body are present, 
but in other organs, like the heart, fewer tissues are required. 

A collection of organs working for the same end or purpose in 
the body is called a system. The heart, arteries, capillaries, and veins, 
for example, have for their common purpose the circulation of the 



b ELEMENTS OF PHYSIOLOGY. 

blood, and together form the circulatory system. In any system, the 
work of each organ must contribute to the work of the system as a 
whole. 

The Plan of the Body. Even a slight knowledge of the 
body reveals such method and order in its manner of doing things that 
the existence of some comprehensive plan of structure and operation 
is at once suggested. Such a plan becomes the more apparent as the 
body is studied in detail, although its full comprehension is still one 
of the unsolved problems of science. An idea of the magnitude of 
the plan of the body may be obtained by simply enumerating the pro- 
visions that are necessary because of the peculiar needs of the cells. 
The cells in all parts of the body must be constantly supplied with 
liquid food and with oxygen and be relieved of waste materials. The 
whole cell group must be moved from place to place. All the parts 
must be warmed and kept at a uniform temperature. Different tis- 
sues must be kept in place and the form of the body preserved, while 
intelligent oversight, management, and protection of the whole group 
is demanded. In brief, the plan of the body must include all pro- 
visions that are necessary for 

The Maintenance of Life. Herein lies the chief difficulty in 
fully understanding the plan of the body. The nature of life is un- 
known. As the biologist sees it, life is a peculiar condition associated 
with protoplasm. When this condition is present, the protoplasm is 
able to manifest its characteristic properties; but when it no longer 
exists, the protoplasm separates into the substances from which it is 
formed. The life condition may, therefore, be regarded as the organ- 
izer and preserver of the protoplasm. The maintenance of life is, of 
course, necessary to the existence of the body, and this is accomplished, 
as before stated, by providing favorable conditions for the cells. 

Chemical Basis of the Body. When life ceases to exist in the protoplasm, 
and the materials forming the body separate, it is observed that one portion passes 
into the atmosphere, another mingles with the soil, and a third portion is water. 
This natural analysis of the body suggests that it is formed of materials that rep- 
resent all three of the states of matter— solids, liquids, and gases. When they are 
subjected to further analysis by the chemist they are found to be made up of a 
number of the simple forms of matter, called elements. Among the more abun- 
dant elements in the body are carbon, hydrogen, oxygen, nitrogen, calcium, and 
phosphorus. Others, like sulphur, iron, magnesium, sodium, chlorine, and potas- 
sium are found in small quantities, while a number of unimportant ones are found 
in traces. None of the elements, however, exist in the body as such, but are com- 



CONSTRUCTION AXD WORK OF THE BODY. 1 

bined with each other to form a great variety of compounds, most of which are 
very complex. These compounds, called the proximate principles, form the chem- 
ical basis of the body and make up the substances both of the cells and the inter- 
cellular material. 

Summary. Physiology is a study of life processes, the physical 
basis of which is protoplasm. This substance is organized into active 
units, called cells, of which there are found in the body several dis- 
tinct varieties or types. Cells that are alike appear in groups, called 
tissues, which possess properties that adapt them to particular pur- 
poses in the body. The tissues are formed into working parts called 
organs and these are further combined into systems. Finally the body 
as a whole is an organization of protoplasm whose parts, although dis- 
similar in structure and function, combine in their several activities 
to perpetuate life. 

Review Questions. 1. Distinguish between general physiology and human 
physiology; between gross anatomy and histology. 

2. Of what value to hygienic living is a knowledge of physiology and 
anatomy ? 

3. Compare tissues with building materials. In what sense do they differ 
from building materials ? 

4. Show that the use made of the tissues is dependent upon their properties. 

5. If a tissue be compared to a brick wall, to what do the separate bricks 
correspond? To what the mortar between the bricks? 

6. Name and give use of each of the parts of a typical cell. 

7. Compare the conditions surrounding a one-celled animal living in the 
water, to the conditions surrounding the cells in a tissue. 

8. State the necessity for the different activities of the cells. 

9. Give the different steps in the organization of protoplasm into the body. 

10. What is an element? Name the four elements most abundant in the 
body. In what form do the elements exist in the body? 

11. Enumerate the provisions in the plan of the body necessary to the 
maintenance of life. 



CHAPTER II. 

THE BLOOD. 

Two liquids of similar nature are found in the body, known as 
the blood and the lymph. The former is kept moving rapidly through 
a system of tubes called the blood vessels, while the latter lies in minute 
spaces in the intercellular material and flows slowly through a second 
system of tubes called the lymphatics. Both liquids minister to the 
wants of the cells. The study of lymph will be deferred to a later 
period. 

The Properties of Blood are shown by the experiments 
which follow. Secure through the assistance of a butcher (see Ap- 
pendix) a bottle of blood which has been allowed to coagulate without 
shaking or stirring ; a bottle of defibrinated blood ; and a bottle of blood 
which has been kept from coagulating by mixing with Epsom salts. 

Experiments. 1. Let some of the defibrinated blood flow (not fall) on the 
surface of water in a glass vessel. Does it remain on the surface or sink to the 
bottom of the vessel? What does the experiment show with reference to the rela- 
tive weight of blood and water ? 

2. Place a small amount of the dark defibrinated blood in a large test tube, 
or bottle, and thin it by adding an equal amount of water. Then place the hand 
over the mouth of the tube and shake until the blood is thoroughly mixed with the 
air in the vessel. Compare with a portion of the blood not mixed with air and 
notice any difference in color. What substance in the air in the test tube probably 
acted on the blood to change its color ? 

3. Fill three tumblers each two-thirds full of water and set in a warm place. 
At intervals of one-half hour pour into each, and thoroughly mix with the water, 
two tablespoonfuls of blood containing the Epsom salts. The water dilutes the 
salts so that coagulation is no longer prevented. Jar the vessel occasionally as 
the coagulation proceeds. After the blood has been added to the last tumbler 
make a comparative study of all. Note that the coagulation begins in all parts of 
the liquid at the same time and that, as the process goes on, the clot shrinks and 
is drawn toward the center. 

4. Place a clot from one of the tumblers in experiment three, in a large ves- 
sel of water. Thoroughly wash, adding fresh water until a clear, white, stringy 
solid remains. This substance is called fibrin and is the cause of the coagulation. 

5. Examine the coagulated blood in the bottle obtained from the butcher. 
Observe the dark central mass (the clot) surrounded by a clear liquid (the 
serum). Sketch the vessel and its contents, showing and naming the two parts 
into which the blood separates by coagulation. 



THE BLOOD. 9 

t 

The foregoing and other experiments show the blood to be heavier 
and denser than water; to have a faint odor and a slightly sweetish 
taste ; to have a bright red color when it contains oxygen and a dark 
red color when oxygen is absent ; and, when exposed to certain con- 
ditions, to undergo a change called coagulation. These properties are 
to be accounted for through the peculiar 

Composition of the Blood. To the naked eye the blood ap- 
pears as a thick but simple liquid. When, however, it is examined 
with a compound microscope, it is seen to be made up of two distinct 
parts — a clear transparent liquid and many small, rounded bodies 
which float in the liquid. The liquid portion is called plasma, the 
small rounded bodies are known as corpuscles. Two varieties of the 
latter are described as reel and white corpuscles. A third variety may 
also be observed under favorable conditions, called blood platelets, in 
addition to some very minute particles or granules. 

Observation. Examine with a compound microscope a small drop of human 
blood. (See Appendix.) If the blood be too thick to distinguish individual cor- 
puscles, it may be diluted with a little water or a small amount of a very 
dilute solution of salt in water. The red corpuscles will appear as amber-col- 
ored, circular, disk-shaped bodies which show a decided tendency to arrange 
themselves in rows, resembling rows of coins. (They do not appear red because 
there is not sufficient coloring matter in single corpuscles.) 

A few white corpuscles may generally be found among the red ones. They are 
easily recognized by their larger size and their silvery appearance which is due to 
the light shining through them. Sketches should be made showing the relative 
size and general arrangement of the corpuscles on the slide. 

Structure and Function of the Red Corpuscles. The 

red corpuscle may be regarded as a single cell, although it has no 
nucleus and is supposed to be without a cell wall. It consists of a 
little mass of elastic and somewhat spongy pro- 
toplasm, called the stroma, which is saturated with 
a reddish coloring matter, called haemoglobin. It 
has the shape of a thin, circular disk with concave 
sides. In size it is about one thirty-two hun- 
dredth of an inch through the long diameter and 
about one-fourth as thick. The red corpuscles are 
_.. . A , r exceedingly numerous, it being; estimated that in 

Fig. 4. A cluster of & J 7 P 

red corpuscles in the health there are as many as five millions in a small 

center of which is a d 

white corpuscle. d r0 p f blood. The number, however, is greatly 

diminished during various forms of disease. 




10 ELEMENT® OF PHYSIOLOGY. 

The function of the red corpuscles is to serve as oxygen carriers 
in the body. They absorb oxygen at the lungs which they give up to 
the cells in the different tissues. They owe this property entirely to 
the presence of the 

Haemoglobin. This substance has the. remarkable property of 
forming, under certain conditions, a weak chemical union with the 
oxygen and, when the conditions are reversed, of separating from 
it. The differences in the conditions to which the blood is subjected, 
at the lungs and in the tissues, will be considered later. The haemo- 
globin forms about nine-tenths of the solid matter of the red corpuscles 
and gives them their color. The stroma, which forms the remainder, 
serves as a contrivance for holding the haemoglobin.* 

Origin of Red Corpuscles. As the red corpuscles are con- 
stantly being destroyed in various ways, new ones have to be regularly 
supplied to take their place. Their origin is not entirely accounted 
for, though the best authorities agree that a large per cent of them 
is formed in the red marrow of the bones. 

The White Corpuscles are irregular in shape and are larger 
than the red ones, their average diameter being about one twenty-five 
hundredth of an inch. They are much less numerous, however, there 
being in healthy blood only about one white corpuscle to every three 
hundred and fifty red corpuscles. They are for this reason, not easily 
observed in the blood. They may be obtained in abundance from 
lymphatic glands. 

Observation. Obtain from a butcher a small piece of the neck sweetbread of 
a calf. Press it between the fingers to squeeze out a whitish, semi-liquid sub- 
stance. Dilute this with water on a glass slide and examine with a compound 
microscope. Xumerous white corpuscles, of different kinds, will be found. Make 
sketches. 

The white corpuscles are endowed to some extent with the power 
of motion and are able to change their shape. For these reasons they 
are migratory in the body, being able to penetrate the walls of small 
blood vessels and to pass between the cells. They collect in large num- 
bers at the parts of the body that may be inflamed and form a consid- 



* A solution of haemoglobin may be prepared by cutting and bruising a blood 
clot in a vessel of water and then straining the liquid through a coarse piece of 
muslin. Such a solution differs from a simple mixture of blood and water in its 
ability to transmit light. Because of its transparency print is easily read through 
it, while the presence of corpuscles would render the liquid opaque. 



THE BLOOD. 11 

erable portion of the white matter found in sores, called pus. They 
originate in the lymphatic nodules. 

Functions of the White Corpuscles. The white corpuscles 
serve a variety of purposes, the following being the most important: 

1. They consume living organisms, known as bacteria, that find 
their way into the blood and cause various diseases. 

2. They form a kind of wall, or covering around any foreign 
substance, such as a splinter, that may penetrate the skin, and prevent 
in this way the spread of poisonous matter through the system. They 
serve a similar purpose in the case of boils and ulcers, isolating as it 
were the infected part from the rest of the body. 

3. They supply an active agent or ferment which, by acting 
on the coagulable material of the blood, causes coagulation. This 
ferment is given up at the time of the escape of blood from wounds 
and because of the injury which the white corpuscles sustain. 

The Plasma is a very complex liquid, consisting of water with 
a large number of substances dissolved in it. The latter may be 
grouped into the following classes : 

1. Albumins, of which three varieties are recognized, known as 
serum albumin, globulin, and fibrinogen. They resemble the white 
of raw egg, and differ in the readiness with which they coagulate.* 
They all serve as food for the cells, while the fibrinogen, in addition to 
this, is the chief agent in the coagulation of the blood. 

2. Carbohydrates and fats. These exist in small quantities in 
the blood and are food for the cells. 

3. Salts. Common salt, or sodium chloride, is the most abun- 
dant member of this class, although several others are present. The 
salts serve various purposes, one of which is to cause the albumins 
to dissolve in the plasma. 

4. Waste products. These are received by the blood from the 
different cells and are carried by the plasma until removed by the 
organs of excretion. 

Cause of Coagulation. Fibrinogen is the coagulable constitu- 
ent of the blood. When exposed to the action of a peculiar chemical 
agent, called fibrin ferment, it readily changes into a white, stringy 
mass known as fibrin. Fibrin ferment does not exist in the blood in its 

* Fibrinogen coagulates more readily than the others and is the only one that 
separates by the ordinary coagulation of the blood. The others remain dissolved 
during this process, but are coagulated by chemical agents and heat. 



12 ELEMENTS OF PHYSIOLOGY. 

normal condition. It is formed, however, when the blood is exposed to 
some influence which causes a disintegration of the white corpuscles 
and blood platelets. Another element which is necessary to the process 
of coagulation is a small amount of calcium. If this is absent, coagu- 
lation does not occur. By the combined action then of the fibrin fer- 
ment and the calcium, the fibrinogen changes into fibrin. This, form- 
ing at first as fine threads throughout the whole mass of blood and en- 
tangling the corpuscles, later contracts and draws the corpuscles into 
the solid mass call the dot. Serum, the liquid squeezed out of the clot 
by the contracting fibrin, contains all the constituents of the plasma 
except the fibrinogen. 

The Purpose of Coagulation is to check the flow of blood 
from small wounds. Clots forming in the mouths of blood vessels when 
they are cut or broken, close them up, and stop the flow of blood which 
would otherwise go on indefinitely. 

The rate of coagulation is increased by heat and retarded by cold. It may be 
prevented entirely by lowering the temperature to near the freezing point. The 
presence of a foreign substance also affects the rapidity of coagulation, and it has 
been observed that bleeding from small wounds is quickly checked by covering 
them with cotton or linen fiber. 

Changes in the Blood. In performing its work in the body the 
must of necessity undergo rapid and continuous change. The 
red corpuscles, whose changes have already been noted, are the most 
stable constituents of the blood. The plasma is the part that is changed 
mc st rapidly. There is, however, such an adequate control of the sup- 
ply of materials to the blood, and of the removal of materials from the 
blood, that its general composition and density do not vary from time to 
time. An excess of certain impurities prompts a greater activity of 
the organs of excretion. If the blood becomes too dense, a feeling of 
thirst prompts one to drink water. Likewise, a scarcity of food mate 
rial causes hunger and a lack of oxygen in the blood induces a desire for 
a deep breath of air. In time of fasting the blood obtains food mate- 
rials from the tissues. Even the quantity of blood remains nearly con- 
stant during the changing conditions of food and water supply, and 
variations in the health and activity of the body. 

The total quantity of blood is estimated at one-thirteenth of the entire weight 
of the body. This for the average individual is an amount weighing nearly twelve 
pounds and having a volume of nearly one and one-half gallons. About forty-six 



TEE BLOOD. 13 

per cent by volume of this amount consists of corpuscles and fifty-four per cent of 
plasma. Of the plasma ten per cent consists of solid materials and ninety per 
cent of water. 

Hygiene of the Blood. An adequate supply of good blood is 
both a safeguard to the health and a most important agent in the re- 
covery from disease. Moreover, the condition of the blood is largely 
dependent upon one's habits of living. From a health standpoint, the 
most important constituents of the blood are the red corpuscles. These 
are generally sufficient in number and vigor in the blood of those who 
take plenty of physical exercise, expose the body freely to outdoor air 
and sunlight, and indulge in plenty of sleep. On the other hand they 
are deficient in quantity and inferior in quality in those who pursue an 
opposite course. Impurities frequently find their way into the blood 
through the digestive organs. One should eat wholesome, well cooked 
food, drink freely of pure water, and limit the quantity of food to what 
can be properly digested. The natural purifiers of the blood are the 
organs of excretion. The skin is one of these and its power to throw 
off impurities depends upon its cleanliness and the activity of the circu- 
lation through it. Alcoholic beverages, if taken in considerable quan- 
tity, have a very injurious effect upon the blood, and interfere with its 
work in the body. 

Patent medicines for purifying the blood, as a rule, do more harm 
than good. One may safely rely upon wholesome food, pure water, 
outdoor exercise, sunlight, plenty of sleep, and a clean skin, for keeping 
the blood in good condition. When these natural agencies fail, a physi- 
cian should be consulted. 

Summary, The blood is a necessary means of supplying condi- 
tions favorable for the cells. It may be regarded as a convenient liquid 
from which they derive their nourishment and into which they expel 
their waste. Its properties and composition are such as to adapt it to 
these purposes and its changes are the unavoidable results of its work in 
the body. 

Review Questions. 1. Compare blood and water with reference to density, 
weight, and complexity of composition. 

2. Compare the red and white corpuscles with reference to size, shape, num- 
ber, origin, and function. 

3. Explain the cause and purpose of coagulation. 

4. After coagulation, what portions of the blood are found in the clot ? 
What portions in the serum? 



li ELEMENTS OF PHYSIOLOGY. 

5. What per cent of the blood (omitting that in the corpuscles) is water? 
What purposes are served by the water in the blood? 

6. Show how the blood, though constantly changing, is kept about the 
same in quantity, density, and composition. 

7. At the lungs the blood changes from a dark to a bright red color and in the 
tissues back to a dark red. What is the cause of these changes? 

8. What property of haemoglobin enables the red corpuscles to serve as an 
oxygen carrier? 

9. What habits must be practiced and what avoided in keeping the blood 
in good condition? 



CHAPTER III. 

CIRCULATION OF THE BLOOD. 

The blood is a moving liquid. Its regular movement through the 
body — starting at one place, flowing out to the different parts and re- 
turning to that place — is termed its circulation. 

The Discovery of the Circulation of the Blood was made in 1616 by an 
English physician named Harvey. In 1619 he taught it in his public lectures and 
in 1628 published the result of his investigations. No other single discovery with 
reference to the human body has proved of so great importance. A knowledge of 
the nature and purpose of the circulation, was the necessary first step in under- 
standing the plan of the body and the method of maintaining life. Hence, physi- 
ology as a science dates from the time of Harvey's discovery. 

The Necessity for the Circulation lies in the fact that the 
blood acts as a carrier for the cells. Oxygen from the lungs, and liquid 
food from the digestive organs, reach the cells through the blood. Like- 
wise, the blood must convey the impurities from the cells to the organs 
of excretion. To accomplish these results the blood must move. So 
great is the necessity for the circulation that its stoppage, for only a 
brief interval of time, results in death. 

The Organs of Circulation, or blood vessels, are of four 
kinds — named the heart, arteries, capillaries, and veins. They serve 
as contrivances both for holding the blood and for keeping it in motion 
through the body. The heart, which is the chief organ for propelling 
the blood, acts as a force pump, w 7 hile the arteries, capillaries, and veins 
serve as tubes for conveying the blood from place to place. All are so 
connected that the blood passes through them in a regular and definite 
order. 

Observation on the Heart. Procure, by the assistance of a butcher, the 
heart of a sheep, calf or hog. To insure the specimen against mutilation, the 
lungs and diaphragm must be left attached to the heart. In studying the different 
parts, good results will be obtained by observing the following order: 

1. Observe the connection of the heart to the lungs, diaphragm, and large 
blood vessels. Inflate the lungs and observe the position of the heart with refer- 
ence to them. 

15 



16 ELEMENTS OF PHYSIOLOGY. 

2. Examine the sac surrounding the heart. It is called the pericardium. 
Pierce its lower portion and collect the pericardial fluid. Increase the opening 
thus made until it is large enough to slip the heart out through it. Slide back the 
pericardium until its attachment to the large blood vessels above the heart is 
found. Observe that a thin layer of it continues down from this attachment, 
making the outer covering of the heart. 

3. Trace out for a short distance and study the veins and arteries connected 
with the heart. The arteries are to be distinguished by their thick walls. Care- 
fully remove and save for later study a section each of an artery and vein, three 
or four inches in length. The heart may now be severed from the lungs by cutting 
the large blood vessels, care being taken to leave a considerable length of each one 
attached to the heart. 

4. Observe the outer portion of the heart. The thick lower portion contains 
the cavities called ventricles; the thin upper ear-shaped portions are the auricles. 
The thicker and denser side lies toward the left of the animal's body and is called 
the left side of the heart; the other is the right side. Locate the right auricle and 
the right ventricle; the left auricle and the left ventricle. 

5. Lay the heart on the table with the front side up and the apex pointing 
from the operator. This places the left side of the heart to his left and the right 
side to his right. Xotice the groove between the ventricles, called the interven- 
tricular groove. Make an incision half an inch to the right of this groove and cut 
towards the base of tha heart until the pulmonary artery is laid open. Then, 
following within about half an inch of the groove, cut down and around the right 
side of the heart. The wall of the right ventricle may now be raised and the 
cavity exposed. Observe the extent of the cavity, its shape, its lining, its columns 
of muscles ( columnae carneae), its half columns of muscles (musculi papillares), 
the tendinous cords (chordae tendinae), the tricuspid valve from the under side, 
etc. Also notice the valve at the beginning of the pulmonary artery, and the 
sinuses or depressions in the artery immediately behind its divisions. 

6. Xow cut through the middle of the loosened ventricular wall from the 
apex into the right auricle, laying it open for observation. Xotice the openings 

(one each for the superior vena cava, the inferior vena cava, and the coronary 
vein) . Compare walls, lining, shape, size, etc., with the ventricle below. 

7. Cut a cross section from the left ventricle about an inch from the apex. 
This will show the extension of the left ventricle to the apex: it will also show 
thickness of its wails and the shape of the cavity. Split up the ventricular wall 
far enough to examine the mitral valve and chordae tendinae from the lower side. 

8. Make an incision in the left auricle. Examine its inner surface and find 
the places of entrance of the pulmonary veins. Examine the mitral valve from 
above. Compare the two sides of the heart part for part. 

0. Separate the aorta from the other blood vessels and cut it entirely free 
from the heart, care being taken to leave enough of the heart attached to the 
artery to insure the semi-lunar valve being left in good condition. After closing 
up the opening- in the sides of the aorta, pour water into the small end and ob- 
-erve the closing of the semi-lunar valve. Repeat the experiment until the action 
of the valve is understood. Sketch the artery showing the valve in a closed condi- 
tion. 



CIRCULATION OF THE BLOOD. 



17 




1. Semi-lunar 
Mitral valve. 
Right ven- 



The Human Heart does not differ materially in structure from 
the heart which has been studied. It is about the size of the clinched 

fist of the owner, and is situated 
very near the center of the tho- 
racic cavity. It is pear-shaped and 
so placed that the small end ex- 
tends downward and to the left. 
Read in some larger work a de- 
scription of the heart, noting the 
structure and location of valves 
and the differences in the struc- 
ture of the walls surrounding the 
-cavities. The general plan of the 
heart and its connections with the 
larger arteries and veins are indi- 
cated in Fig. 5. 

The pericardium forms a 
protective covering for the 
heart. It consists of a closed sac 
so arranged as to form a double layer around the heart. The inner 
layer blends closely with the tissues of the heart, forming its exterior 
lining. The outer layer loosely surrounds the other and connects at 
places with the membranes of the lungs. The free surfaces secrete a 
small quantity of liquid which occupies the pericardial sac and prevents 
friction in the heart's movements. 

How the Heart Does Its Work. The heart is a hollow mus- 
cle and does its work by contracting and relaxing. When it contracts, 
its cavities are closed and the blood is forced from them. When it 
relaxes the cavities open and the blood flows in to refill them. Valves 
prevent the backward flow of blood. The heart's action may be readily 
illustrated in the following manner : 

Procure a syringe bulb with an opening in each end. Attach a rubber tube 
to each end of the bulb, letting the tubes reach into two tumblers containing water. 
By alternately compressing and releasing the bulb water is pumped from one ves- 
sel into the other. The bulb may be taken to represent one of the ventricles. 
What action of the ventricle is represented by compressing the bulb ? By releasing 
the pressure? 

By making the proper connections with a greater length of tubing, and filling 
the whole with water, the entire circulation may be represented. Show by a sec- 
tional drawing the arrangement of the valves in the syringe bulb. 

2 



Fig. 5. Diagram of the heart, 
valves. 2. Tricuspid valve. 3. 
4. Right auricle. 5. 'Left auricle, 
tricle. 7. Left ventricle. 8. Chordae tendinae. 
9. Inferior vena cava. 10. Superior vena cava. 
11. Pulmonary artery. 12. Aorta. 13. Pulmonary 
veins. 



IS 



ELEMEXTS OF PHYSIOLOGY. 



The Arteries and Veins form two systems of tubes which ex- 
tend, by their divisions, from the heart to all parts of the body. The 
arteries receive the blood from the heart and distribute it to the capil- 
laries. The veins receive the blood from the capillaries and return it 
to the heart. 

Observation. Examine carefully the artery and vein saved from the dissec- 
tion of the heart. Compare them with reference to the thickness, elasticity, and 
toughness of their walls. Which is able to stand open? After allowing them to 
lie in water over night separate each into its layers or coats. 

Both arteries and veins have three coats. The inner coat consists 
of thin, flat cells, united at their edges and is continuous with the lining 
membrane of the heart. The middle coat consists mainly of non- 
striated muscular tissue. In the artery it is very thick. The outer 
coat is largely connective tissue. 

The arteries and veins differ in several important respects and are 
easily distinguished. The walls of the arteries are thicker and heavier 
than those of the veins. They are also highly elastic, while the veins 
are but slightly elastic. On the other hand, many veins contain valves 
and the entire venous system holds more blood than the system of 
arteries. 

Experiment. Close up the small end of the aorta, which was cut from the 
heart during its dissection and which has in it the semi-lunar valve, with a close- 
fitting cork having two openings. In one 
opening a pointed glass tube should be 
fitted and in the other a straight glass 
tube for attaching it by a rubber tube 
with a syringe bulb., or force-pump. 
Force water into the artery and observe : 
1. That the artery swells and may be 
filled overfull. 2. That the water is 
forced out through the small tube when 
there is no pressure from the pump. (The 
small arteries branching from the aorta, 
should be tied or plugged before forcing 
in the water.! 




Fig. ( 
arteries 



Illustrating the elasticity of 
See experiment. 



The Advantage of the Elasticity of the Arteries is two- 
fold: 1. It prevents the bursting of the arteries when the blood is 
emptied into them from the ventricles. 2. It is a means of keeping 
the blood in the arteries under continuous pressure, although the ven- 
tricles exert their pressure only at intervals. During the contraction 
of the ventricles the arteries are filled over-full and have to swell out to 



CIRCULATION OF THE BLOOD. 19 

make room for the excess of blood. Then while the ventricles are 
relaxing, the arteries exert their elastic force to keep the blood flowing 
steadily into the capillaries. In thus causing an otherwise intermitteut 
flow to become a continuous and steady stream, the elasticity of the 
artery serves a purpose similar to that of the air-chamber of a force- 
pump. 

The Valves in the Veins enable pressure at different parts of 
the body to force the blood toward the heart. The muscles, for exam- 
ple, in contracting, press against the sides of the veins and tend to 
empty them at those places. Since the valves are closed by any back- 
ward movement, the force of the muscle can drive the blood in but one 
direction and that is toward the heart. Scarcely a movement of the 
body can be made without compressing the veins at some point and, as a 
rule, the valves are found in greatest abundance where the compressions 
are most likely, to occur. The valves in the veins are, therefore, an 
economical device to enable pressure, that would otherwise interfere 
with the circulation, to assist in the process. 

Observations. Exercise the arm a few minutes to increase its blood supply. 
Expose the forearm and examine the veins on its surface. With the finger stroke 
one of the veins toward the shoulder. Much of the blood can be forced out of it. 
Now stroke the vein toward the hand. The blood is not forced backward but the 
vein swells instead, the swelling being greatest at one or two places resembling 
"knots." These knots mark the position of valves which prevent the return of 
blood to the hand. 

The Muscular Coat serves two important purposes. In the 
first place it, together with the elastic tissue, keeps the capacity* of 
the blood vessels equal to the volume of the blood that is circulating. In 
the second place it serves as the active agent in regulating the amount of 
blood that goes to a given organ. It accomplishes the latter purpose by 
varying the capacity of the artery going to the organ. To increase the 
blood supply the muscle relaxes and the artery is dilated by the blood 
pressure within. To diminish the supply the muscle contracts making 
the capacity of the artery less. The muscular coat receives nerves from 
the central nervous system by which it is controlled. 



* The total capacity of the blood vessels is considerably greater than the vol- 
ume of blood which they contain. It is only by keeping their walls contracted or 
in a condition of '"tone" that the pressure from the heart can be transmitted to 
all parts of the blood stream and the circulation be maintained. 



20 ELEMENTS OF PHYSIOLOGY. 

Important Arteries and Veins. The two main arteries are 
the pulmonary artery and the aorta. The first receives blood from the 
right auricle and, through its divisions, passes it to all parts of the 
lungs. The second receives the blood from the left ventricle and, by 
its branches, distributes it through the entire body. 

The most important veins are the pulmonary (usually four, but 
sometimes three, in number) which pass the blood from the capillaries 
of the lungs to the left auricle, the superior vena cava which connects 
with the right auricle from above, and the inferior vena cava which 
joins the right auricle from below. The superior vena cava is formed 
by the union of veins from the arms, head, and upper part of the trunk, 
while the inferior vena cava is formed by the union of veins from the 
lower extremities, and the middle and lower part of the trunk. The 
portal vein, because of its size and function, is also of considerable 
importance. It receives blood from the stomach, intestines, and other 
abdominal organs and conveys it to the liver. 

The Capillaries consist of a network of minute blood vessels 
which connect the terminations of the smallest arteries with the begin- 
nings of the smallest veins. They have an average diameter of less 
than one two-thousandths of an inch, and their walls consist of a 
thin layer of cells placed edge to edge. This structure renders them 
porous, and enables the plasma of the blood and the white corpuscles to 
penetrate their walls. With a few exceptions, they are found in great 
abundance in all parts of the body. 

Observation. Study with a compound microscope the circulation of the 
blood through the capillaries in the web of a frog's foot. For an extended exami- 
nation it is best to destroy the frog's brain. (See Appendix.) The frog may be 
attached to a thin board which has an opening in one end over which the web of 
the foot may be stretched. Threads should extend from two of the toes to pins 
driven in the board to secure the necessary tension of the web and the foot and 
lower leg should be kept moist. By careful work single capillaries may be traced 
back to the small arteries from which they branch, and forward to the veins which 
they help to form. The appearance is truly wonderful, but allowance must be 
made for the fact that the motion of the blood is magnified and that it moves 
much more slowly than it appears to. 

Functions of the Capillaries. Because of the thinness of 
the capillary walls and their porous structure, liquids readily penetrate 
them. This enables the capillaries to serve the two-fold purpose of 
admitting substances into the blood and of passing substances from the 



CIRCULATION OF TEE BLOOD. 



21 



blood. In the absorption of liquids at the digestive organs and of 
oxygen at the lungs they serve the former purpose and in the distribu- 
tion of substances at the various tissues, the latter. It is only at the 
capillaries that the blood is able to receive and give up its constituents. 
In addition to this function the capillaries, by the degree to which they 
penetrate the various tissues, bring the blood very near the individual 
cells. 

Divisions of the Circulation. Man, in common with all warm- 
blooded animals, has a double circulation, a fact which explains the 

double structure of the heart. The 
two divisions are known as the pul- 
monary and systemic circulations. 
By the former the blood passes from 
the right ventricle through the lungs 
and is then returned to the left auri- 
cle; by the latter it passes from the 
left ventricle through all parts of the 
body, returning to the right auricle . 
All of the blood flows continuously 
through both circulations and passes 
the various places in the following 
order : Right auricle, tricuspid valve, 
right ventricle, right semi-lunar 
valve, pulmonary artery and its 
branches, capillaries of lungs, pul- 
monary veins, left auricle, mitral 
valve, left ventricle, left semi-lunar 
valve, aorta and branches, systemic 
capillaries, veins, superior and infe- 
rior venae cavae and then again into 
the right auricle. At the lungs the 
blood gives up carbon dioxide and re- 
ceives oxygen. In the systemic capillaries it gives up its oxygen and 
receives carbon dioxide and other impurities. 

In addition to the two main divisions of the circulation, special 
modifications of the general plan are found in various places. Such a 
modification in the liver is called the portal circulation and another in 
the kidneys is termed the renal circulation. To some extent the blood 




Fig. 7. Diagram of the circulation. 1. 
Systemic divisions. 2. Pulmonary divis- 
ion. 3. Through the kidneys. 4. Portal 
circulation. 5. Visceral circulation. 6. 
Connection with the lymph vessels. 8. 
Aorta. 



22 ELEMENTS OF PHYSIOLOGY. 

supply of the avails of the heart is outside of the general plan, and has 
been designated the coronary circulation. 

Hygiene of the Circulatory Organs. The heart being a 
muscle, is subject to the laws of muscular exercise. It may be injured 
by over-exertion but is strengthened by a moderate increase in its usual 
work. It may even be subjected to great exertion without danger by 
gradually increasing the amount of work that devolves upon it. Such 
a course, by giving the heart time to gain in size and strength, prepares 
it for tasks that could not at first be attempted. Injury is frequently 
done the heart of the amateur athlete, bicyclist, or mountain climber, 
through attempting more than the previous training warrants. Active 
exercise during short periods, followed by intervals of rest, such as the 
exercise furnished by the climbing of stairs, or by short runs, is consid- 
ered the best means of strengthening the heart. 

Since the heart is controlled by the nervous system, it frequently 
becomes irregular in its action through nervous disorders. It is 
through their effect upon the nervous system that worry, over-study, 
undue excitement, or dissipation, cause disturbances of the heart. In 
all such cases the remedy lies in the removal of the cause. A number 
of drugs, among which is alcohol, interfere, through their effect upon 
the nerves, with the normal action of the heart. The nicotine of 
tobacco produces an undesirable effect in two ways : 1. Where the use 
of tobacco is begun in early life, it interferes with the normal develop- 
ment of the heart muscle, leading to marked weakness in the adult. 
2. When used in considerable quantity by young or old, it induces a 
distressing nervous condition, known as the "tobacco heart." Coffee 
used to excess, also interferes with the nervous control of the heart. 

The presence of valves in the veins shows that part of the force to 
move the blood should come from the bodily movements. While the 
heart is able to propel the blood when the body is in a condition of 
repose, the benefit of different movements, as utilized by the valves, 
cannot be doubted. Daily physical exercise may, therefore, be looked 
upon as a necessary condition for the efficient and healthful circulation 
of the blood. 

Suggested Topics for Further Study. 1. Quantity of work performed by 
the heart. 

2. Sounds of the heart. 

3. Effect of bodily exercise on the activity of the heart. — Count the number 



CIRCULATION OF THE BLOOD. 23 

of pulsations per minute (a) when in a sitting posture, (b) when standing, (c) 
after walking, and (d) after running. 

4. Circulatory systems of other animals. — Compare the systems of the 
insect, fish, reptile, and warm-blooded animal. 

5. Methods of checking the flow of blood from wounds. 

6. Variations in blood pressure and velocity in the arteries, veins, and 
capillaries. 

Summary. The blood, to serve as a carrier of materials to and 
from the cells, nrnst be kept moving throughout the entire body. The 
blood vessels contain the blood, supply the channels and the force neces- 
sary for its circulation, and provide conditions for the entrance of 
materials into, and their exit from the blood. The heart is the chief 
factor in propelling the blood, although the muscles and elastic tissue 
in the arterial walls and the, valves in the veins are necessary aids in 
the process. At the capillaries the blood takes on and gives off mater- 
ials. The arteries and veins serve chiefly as tubes for transferring 
the blood from place to place. All the organs of circulation are under 
the control of the nervous system. 

Review Questions. 1. Of what special value to the study of the body, 
was the discovery of the circulation of the blood? 

2. State the necessity for a circulating liquid in the body. 

3. Show by a drawing the general plan of the heart, locating and naming 
the essential parts. 

4. Explaiir the heart's method of propelling a liquid. 

5. Of what use are the valves in the heart? In the veins? 

6. Why should there be a difference in structure between the two sides of 
the heart? 

7. Of what advantage is the elasticity of the arteries? 

8. State the purpose of the muscular coat. 

9. How is the blood forced from the capillaries back to the heart ? 

10. If the rest period following each contraction of the heart is one-third 
as long as the period of contraction, how many hours is the heart able to rest 
out of every twenty-four? 

11. State the functions of the capillaries. 

12. Trace the blood through a complete circulation, beginning with the 
left auricle. 

13. What physical exercises tend to strengthen the heart? What ones tend 
to injure it? 

14. State the effects of tobacco upon the heart. 



CHAPTER IV. 

LYMPH AND THE LYMPHATICS. 

Necessity for the Lymph. The blood, it will be remembered, 
moves everywhere through the body in a system of closed tubes. It can 
therefore come in contact only with those cells which line the blood 
vessels. The capillaries, to be sure, bring the blood very near the cells 
of the different tissues ; still there is need of a liquid to fill the space 
between them and the cells and to transfer materials from one to the 
other. The lymph occupies this position and does this work. The 
position of the lymph with reference to the capillaries and cells is shown 
in Fig. 10. 

Origin of the Lymph. The chief source of the lymph is the 
plasma of the blood. As before described, the walls of the capillaries 
consist of a single layer of thin cells placed edge to edge. Partly on 
account of the pressure upon the blood and partly on account of the 
natural tendency of liquids to pass through animal membranes, a con- 
siderable portion of the plasma penetrates the thin walls and enters the 
spaces occupied by the lymph. 

Another source of lymph is material from the cells. This is of the 
nature of waste, but it adds to the bulk of the lymph. A considerable 
portion of the material absorbed from the alimentary canal, as well as 
liquids absorbed through the skin, also enter the lymph before passing 
into the blood. The lymph, however, consists chiefly of the blood 
plasma that has passed through capillary walls. 

The Composition of the Lymph, as would be expected, is 
quite similar to that of the blood. In fact, nearly all the important 
constituents of the blood are found in the lymph, but in different pro- 
portions. Food materials for the cells exist in smaller proportions than 
in the blood, while the impurities from the cells exist in larger propor- 
tions. As a rule the red corpuscles are absent from the lymph, but the 
white corpuscles are found there in greater abundance than in the blood. 

Physical Properties. The lymph is a colorless and slightly 
alkaline liquid, heavier and denser than water, though not so dense as 

24 



LYMPH AND THE LYMPHATICS. 



25 




Fig. 8. Connection of the main lymphatic ducts 
with the circulation. 1. Superior vena cava. 2. Tho- 
racic duct. 3. Right lymphatic duct. 4. Right subclavian 
vein. 5. Left subclavian vein. 



blood. It has the power of coagulating, but coagulates more slowly 
than blood. 

Kinds of Lymph Vessels. Most of the lymph of the body lies 
in the minute cavities surrounding the cells. These are called lymph 

spaces and correspond, in 
a way, to the capillaries. 
Connected with these are 
a great number of slender 
tubes, with thin walls, call- 
ed lymphatics. These re- 
semble veins in purpose 
and, like the veins, have 
valves. They differ from 
veins, however, in being 
more uniform in size, and 
in having very thin walls. 

The various lymphat- 
ics in different parts unite 
with each other to form 
slightly larger vessel's, and 
these gradually converge toward, and empty into, the two main lymph 
tubes of the body. The smaller of these, called the right lymphatic 
duct, represents the convergence of the lymph vessels of the right arm, 
the right side of the head, and the region of the right shoulder and it 
empties into the right subclavian vein. The larger, known as the 
thoracic duct, connects with the lymph tubes in the remaining parts 
of the body and empties into the left subclavian vein. Fig. 8. 

The lymph tubes that join the thoracic duct from the small intestine are 
called lacteals. While these do not differ in structure from the tubes in the 
other parts of the body, they perform a special work in the absorption of fat. 

Movements of the Lymph. Though the lymph may be re- 
garded as a comparatively quiet liquid, it has three well defined move- 
ments, as follows : 1. That of a current passing from the capillaries 
toward the cells. 2. A current which moves from the cells toward the 
capillaries. 3. A movement of the entire body of lymph along the 
lymph channels, toward the larger lymph vessels. Fig. 10. 

Return of the Lymph to the Blood. The lymph vessels are 
generally regarded as a division of the circulatory system, and the 
lymph may be looked upon as a portion of the blood which will, 



26 ELEMENTS OF PHYSIOLOGY. 

sooner or later, return to the blood vessels. A large part of the lymph 
re-enters the blood at the capillaries, by the process of osmosis, while the 
remainder finds its way back through the lymph channels. The latter 
passes first from the lymph spaces into the lymphatics. It then moves 
through these tubes until it enters either the thoracic duct or the right 
lymphatic duct. From these it flows into the subclavian veins. Fig. 8. 

Causes of the Flow of Lymph. There is no force pump, 
like the heart, connected with the lymphatics, and the flow of the 
lymph is brought about by forces which act indirectly. The more 
important of these are the following : 1. Blood pressure in the capil- 
laries. The plasma which is forced through the capillaries by pres- 
sure from the heart makes room for itself by pushing 
a portion of the lymph out of the lymph spaces. 
This in turn presses upon the lymph in the tubes 
which it enters. In this way pressure from the 
heart may be transmitted to the lymph. 2. By va- 
riable pressure on the walls of the lymph tubes. The 
pressure exerted on the sides of the lymph tubes, by 
contracting muscles, will close them at certain points, 
and push the lymph past valves which prevent its re- 
turn. Pressure at the surface of the body, pro- 
vided that it is variable, also forces the lymph toward 
the heart. The valves serve the same purpose in 
Fig-. 9. illustrating the lymph vessels as in the veins. 3. The inspira- 
de e s a S 10 propeiiing m t U h S e tory force. When the thoracic cavity is enlarged, 
in breathing, unbalanced atmospheric pressure forces 
the lymph toward the cavity, and into the veins, in the same manner 
that it forces air into the lungs. 

The Lymphatic Glands, or lymphatic nodules, are small, rounded bodies 
situated along the course of the lymph tubes. They vary in size, some of the 
largest being an inch or more in length. The lymphatic vessels generally open 
into them on one side and leave them on the other. They are not glands in 
function, but are so called because of their having the general form of glands. 
They provide favorable conditions for the development of white corpuscles. (P. 
10.) 

Interchange of Materials at the Cells. Food substances 
and oxygen in passing from the blood through the lymph into the 
cells must penetrate both the wall of the capillary and that of the cell. 
These are likewise penetrated by the impurities which flow from the 
cells back to the blood. The passage of these substances occurs, in 




LYMPH AND THE LYMPHATICS. 27 

part at least, in accordance with the principle known as osmosis, or 
dialysis. 

Osmosis Illustrated. If a vessel with an upright, membra- 
nous partition be filled on the one side with pure water and on the 
other with water containing salt, an interchange of material will take 
place through the membrane until the same proportion of salt exists on 
the two sides. Osmosis is also illustrated by the following 

Experiment: Separate the shell from the lining membrane at one end of 
an egg, over an area an inch in diameter. To do this without injuring the 
membrane, the shell must first be broken into small pieces and then picked off 
with a pair of forceps, or a small knife blade. Fit a small glass tube, eight 
inches long, into the other end so that it shall penetrate the membrane and 
pass down into the yolk. Securely fasten the tube to the shell by melting bees- 
wax around it, and set the egg in a small tumbler partly filled with water. 
Examine in the course of half an hour. Whac evidence now exists that water 
has passed through the membrane into the eggl 

The Conditions under which Osmosis Occurs are as fol- 
lows : 1. The liquids on the two sides of the membrane must be 
unlike either in composition or in density. In case of a difference 
in density the greater flow of liquid is toward the denser substance. 
2. The liquids must be capable of wetting or penetrating the mem- 
brane. If but one liquid penetrates the membrane the flow will take 
place in one direction only. 3. The liquids must be of such a nature 
as to mix readily. 

Osmosis at the Cells. Oxygen and food materials which are 
found in great abundance in the blood, are 
B/aod ( Cells I o ( ^ ess abundant in the lymph and still less 
abundant in the cells. According to the prin- 
ciple of osmosis* the flow of oxygen and food 
materials will be from' the capillaries toward 
the cells. On the other hand the impurities 
are most abundant in the cells where they are 
formed, less abundant in the lymph, and least 
abundant in the blood. Hence the impuri- 
lym^i to"the e bfoo°d n and thl ties will flow from the cells toward the cap- 
illaries. Tig 10. 
The Work of Water both in the exchanges at the cells and in 

*The interchange of materials through membranous walls is not fully ac- 
counted for by osmosis alone and it is quite probable that other forces are 
concerned in the process. 




28 ELEMENTS OF PHYSIOLOGY. 

the circulation of the blood and the lymph may here be noted. The 
solid substances in these liquids are either dissolved in or floated by 
the water and by it are carried along. 

In this way water serves as a transporting and distributing 
agent without which the exchanges at the cells and between different 
parts of the body would be impossible. 

Summary . The exchange of materials, between the cells and the 
blood, takes place through the lymph. Its composition and location 
adapt it to this purpose. It consists chiefly of escaped blood plasma, 
while the vessels that contain it are a part of the general circulatory 
system. The lymph is continually finding its way, through suitable 
channels, back into the blood stream. 

Review Questions. 1. State the necessity for the lymph in the body. 

2. Compare lymph and water with reference to density, color, and composi- 
tion. 

3. Compare blood and lymph with reference to composition, physical prop- 
erties, and movement through the body. 

4. Compare the lymph tubes and the blood vessels with reference to gen- 
eral structure and the different kinds. 

5. Show how blood pressure at the capillaries causes a flow of the lymph. 
G. Trace the lymph in its flow from the right hand to where it enters 

the blood. From the feet to where it enters the blood. 

7. What conditions prevail at the cells to keep the oxygen continually flow- 
ing in one direction and impurities in the opposite direction? 

8. What part does water play in the exchanges at the cells? 



CHAPTER V. 

RESPIRATION. 

Through the circulation of the blood and the lymph, the cells in 
all the tissues are placed in communication with the surface of the 
body. Any substance which enters the blood at the surface will be 
carried to the cells. On the other hand, any substance which enters 
the blood at the cells may be carried to the surface and there removed 
from the body. It is now our purpose to consider some of the materials 
that are made to pass from the outside of the body to the cells and 
vice versa. Two of these substances are constituents of the atmos- 
phere. 

The Atmosphere, or air, completely surrounds the earth, as 
a kind of envelope, and comes in contact with everything upon its 
surface. It is composed chiefly of two colorless gases known as oxygen 
and nitrogen, but it also contains minute portions of other substances 
such as carbon dioxide and watery vapor. Because of its weight it 
exerts continuous pressure which, at sea level, amounts to nearly fif- 
teen pounds to the square inch. The atmosphere forms an essential 
part of one's physical environment and serves the body in various ways. 

Respiration, or breathing, is carried on by alternately taking 
air into and expelling it from special contrivances in the body, called 
the lungs. The act of taking air into the lungs is known as inspira- 
tion; that of expelling it, expiration. 

The Purpose of Respiration, as indicated by the changes 
which air undergoes in the lungs, may be shown by the following 

Experiments: 1. Fill a quart jar even full of water. Place a heavy 
piece of cardboard over its mouth and invert it, without spilling, in a pan of 
water. Inserting a tube under the jar, blow air, that has been held as long as 
possible in the lungs, into the jar. When filled with air, remove the jar from 
the pan, but keep the top well covered. Slipping the cover slightly to one side, 
insert a burning splinter and observe that the flame is extinguished. This proves 
the absence of sufficient oxygen to support combustion. Pour in a little lime-water 

29 



30 ELEMENTS OF PHYSIOLOGY. 

(see Appendix) and shake to mix with the air. The change of the lime-water 
to a milky white color indicates the presence of carbon dioxide. 

2. Blow the breath against a cold window pane. Note and account for 
the collection of moisture. 

Air taken into the lungs in ordinary breathing, parts with about 
five per cent of itself in the form of oxygen and receives about four 
per cent of carbon dioxide, and a small quantity of watery vapor, 
These changes suggest a two-fold purpose of respiration: 

1. To obtain from the atmosphere the supply of oxygen needed 
in the body. 2. To transfer to the atmosphere certain materials 
(waste products) which must be removed from the body. 

The Respiratory Organs, taken together, form an apparatus 
for dealing with matter in the gaseous state and are constructed with 
reference to the properties of the atmosphere. They include the fol- 
lowing parts: 

1. A special arrangement of moist vascular membrane which 
enables the air to come very near a large surface of the blood. 

2. A system of air passages, or tubes, which connect this vas- 
cular surface with the outside atmosphere. 

3. The thorax which provides a cavity for holding the principal 
organs of respiration and to which is attached 

4. A muscular mechanism which forces the air through the air 
passages. 

5. A nervous mechanism which regulates the respiratory move- 
ments. 

These parts are more or less combined in, and their action cen- 
tered around, what is recognized as the special organ of respiration, 
called 

The Lungs. The lungs consist of two sac-like bodies which 
are suspended in the thoracic cavity and which occupy most of the 
space not taken up by the heart. 

Observation. Secure from a butcher the lungs of a sheep, calf, or hog. 
The windpipe and heart should be left attached and the specimen kept in a 
moist condition until used. Study in the following order: 

1. Examine the large open tube (consisting of the larynx and the trachea) 
and the closed tube lying back of it (the oesophagus). Observe the cartilag- 
inous plates in the larynx and the rings in the trachea. What purpose do they 
serve? Remove and make a drawing of a ring of the trachea. 

2. Insert a tube ir. the trachea and innate the lungs, noting the number 
of times their volume is thus increased. 



RESPIRATION. 



31 



3. Examine the thin membrane (the pleura) inclosing the lungs. Strip 
off a piece and test its elasticity. 

4. Sever the small upper lobe from the remainder by cutting the bronchial 
tube. Split this tube a short distance into the lung, observing its smooth lining 
and the openings of the smaller tubes or branches from it. Are the rings in 
these like those of the trachea ? Make cross sections of this portion of the 
lung and find the openings of the lesser bronchial tubes. 

5. Follow the trachea down to where it branches to form the bronchi. Find 
a branch of the pulmonary artery which approaches one of the bronchi and trace 
both the bronciius and artery into the lung. Observe that as one branches the 
other branches, until the smallest divisions are reached. The pulmonary veins 
also lie alongside the bronchial tubes, but are not so easily traced as the 
arteries. 

6. Place a piece of lung upon water. In floating what portion is submerged ? 
Inference. 

The lungs represent the combined mass of many air sacs, together 
with the air tubes and blood vessels associated with them. (Eead 
the general description of the lungs and air passages in some larger 
work. ) 

The Air Passages provide a continuous passageway between 
all parts of the lungs and the outside atmosphere, through which air 
is passed in both directions. The separate parts which form the 
passages, named in the order that air goes through them, in entering 
the lungs, are the nostrils, pharynx, larynx, 
trachea, bronchial tubes, and the lesser bron- 
chial tubes. Only the upper part of the 
pharynx can be properly classed as an air pas- 
sage. The lower portion is a part of the food 
canal, while the middle provides a suitable 
cross-roads for the air tract and the passageway 
of the food. Fig. 11. Air may also enter the 
pharynx through the mouth. This is necessary 
in many instances, but in ordinary breathing is 
objectionable. The larynx, in addition to be- 
ing an air passage, serves as the organ of the 
voice. 

Additional Work of the Air Passages. The air is pre- 
pared in going through the different passages for entrance into the more 
delicate portions of the lungs. Especially must it be changed in 
temperature and in the amount of moisture that it contains and also, 
in many instances, freed from dust particles. A large amount of 




Fig. 11. Relation of 
the pharynx to other 
passages. 1. Pharynx. 2. 
Larynx. 3. Oesophagus. 
4. Trachea. 5. Nostril. 
6. Mouth. 7. Eustachian 
tube. 8. Lachrymal duct. 





32 ELEMENTS OF PHYSIOLOGY. 

this preparatory work is done in the nostrils where the air is made 
to pass over a large surface of warm and moist mucous membrane. 
For this reason breathing should be through the nostrils. 

To enable the air to move easily through the different passages 
it is necessary that they be kept open and clean. They are kept 
open by special contrivances found in their walls. In the trachea, 

bronchi, and larger bronchial tubes 
(M«M}h* these consist of imperfect rings of car- 

tilage. In the small tubes moat of the 
cartilage disappears, its place being 
taken by connective tissue. The walls 
of the larynx contain strips and plates 
of cartilage, while the nostrils and 
pharynx are kept open by their bony 
surroundings. 

The air passages are kept clean 

bv cells adapted especiallv to that pur- 

&2JSTV*S??2S^ a Pose, known as the ciliated epithelial 

smaii air tube. cells> The peculiarity of these cells 

is their small hair-like projections called cilia. These cells line the 
mucous membrane in most of the air passages and are so placed that 
the cilia extend into the open space in the tubes. Tig. 12. The cilia 
keep up an inward and outward wave-like motion which has greater force 
in the outward direction. The effect of this is to carry any foreign 
matter, such as dust particles and bits of partly dried mucus or phlegm, 
to where it may be easily expelled from the lungs. 

Terminal Air Spaces, Each of the smallest divisions of the 
bronchial tubes terminates in a sac-like 
enlargement, called the infundibulum. 
This by a process of infolding divides 
its inclosed space into a number of 
small rounded cavities which are known 

as the air-cells, or alveoli. These vary T" - ^ — ^^V^^^^ 
somewhat in shape and size, the aver- ^ ^^^o^ 

aes beinsr about one one-hundredth -.«.,. , „«, 

Fig. 13. Terminal air space. 

of an inch in diameter. Fig. 13. 

Each alveolus is surrounded by a delicate wall of elastic connective 

tissue which supports a dense network of capillaries and is lined by a 

_ layer of flat cells placed edge to edge. This arrangement brings 




RESPIRATION. 



33 



air very near a large surface of blood and makes possible the exchange 
of gases. At no place in the lungs, however, does the air come in direct 
contact with the blood but their exchanges always take place through 
both the capillary walls and the walls of the alveoli. 

Observation. Inflate the lungs of some small animal, as a cat or rabbit, 
and examine the divisions as they may be seen at the surface. The smaller 
divisions are the alveoli; the larger ones the infundibula. 

The Blood Supply of the Lungs. The pulmonary artery 
and its branches convey the blood from the right ventricle to all parts 

of the lungs. The branches lie 
alongside of and divide simi- 
larly to the bronchial tubes, and 
finally join the capillaries that 
surround the alveoli with which 
the lesser bronchial tubes con- 
nect, From the capillaries the 
blood is returned to the heart 
by the pulmonary veins. These 
lie alongside of the arteries and 
bronchial tubes and unite to 
form the veins which empty 
. their contents into the left au- 
ricle. This arrangement brings 
practically all the blood through 
the capillaries that surround the 
terminal air spaces. Fig. 14. 

The lungs also receive 
blood, through small branches 
from the aorta, which supplies 
nourishment to the different 




Fig. 14. Diagram of the lungs. 1. Branches 
of the pulmonary artery. 2. Pulmonary veins. 3. 
Terminal air space. 4. Bronchial tubes. 5. 
Bronchi. 6. Trachea. 7. Larynx. 

The arrows indicate the movements of the air 
and the blood. 



parts. 



The Thorax, or chest, is that part of the trunk between the 
neck and the abdomen which incloses a space known as the thoracic 
cavity. The framework of the thorax is furnished by the ribs, the 
portion of the spinal column with which the ribs connect, and the 
sternum or breastbone. The ribs form gliding joints with the spinal 
column and connect with the sternum in front by strips of cartilage. 
They do not encircle the thoracic cavity in a horizontal direction but 
3 



34 ELEMENTS OF PHYSIOLOGY. 

slant downward and outward from the back. Attached to the ribs are 
many small muscles which, by their contraction, elevate the ribs and 
expand the chest. The thoracic cavity is separated from the cavity 
below by a movable partition, called 

The Diaphragm. The margins of the diaphragm are firmly 
attached to the walls of ' the thorax at the place where they blend 
with the walls of the abdomen. Its outer margin is muscular, while 
the central portion consists of a heavy sheet of connective tissue. 
The diaphragm is in an arched condition, being kept in this form by 
pressure from the organs below and by its connection above with the 
membrane of the thoracic cavity, known as 

The Pleura. This is a thin and elastic, but tough membrane 
which covers the outside of the lungs and lines the inside of the chest 
walls. The layer covering each lung is continuous with that of the 
chest wall on the same side and forms with it a closed sac by which 
the lung is surrounded. Properly speaking then, there are two pleurae 
and these, besides inclosing the two lungs, partition off a middle space 
which is occupied by the heart. Each pleura also covers the upper 
surface of the diaphragm on the same side and then deflects upward 
from the center to join the pericardium. A small amount of liquid 
is secreted by the pleural lining which prevents friction as the sur- 
faces glide over each other in breathing. 

How Air is Brought into and Expelled from the Lungs. 

The principle involved in breathing is that air flows from a place of 
greater to a place of less pressure. The construction of the thorax 
adapts it to the application of this principle. Its walls are air-tight 
and it is able, by changing the size of the cavity within it, to produce 
alternately a place of less and a place of slightly greater pressure than 
that of the atmosphere on the outside of the body. 

The lungs are suspended from the upper portion of the thoracic 
cavity and are always sufficiently filled with air to keep their outer 
surface pressed against the chest walls. The trachea and the upper 
air passages provide the only opening to the outside atmosphere. When 
the thorax is enlarged, making an area of less pressure within, the 
greater pressure of the atmosphere on the outside, forces the air into 
the lungs, causing them to expand and fill the extra space within 
the cavity. When the thorax is diminished in size the air within the 
lungs is slightly compressed, causing it to exert greater pressure by its 



RESPIRATION. 



35 



elastic force than the atmosphere exerts on the outside. This causes 
air to flow out until the equality of pressure is again restored. 

In this connection a hand bellows, such as Is 
used in kindling fires, may be studied with profit, 
its action being similar to that of the thorax. Ob- 
serve that when the sides are spread apart air flows 
into the bellows. When they are pressed together 
the air flows out. If a sac be hung in the bellows 
with its mouth attached to the projecting tube and 
the valve in the side of the bellows closed it would 
represent almost exactly the plan of the breathing 
organs. Fig. 15. 

Experiment. With a tape line take the cir- 
cumference of the chest of a boy, when he has 
expelled from the lungs all the air possible. Take 
it again when he has them inflated to their utmost 
capacity. The difference in the measurements 
represents the change of chest capacity. What does 
this experiment show with reference to the cause 
of breathing? 




Fig. 15. The respiratory and 
the hand bellows. Compare part 
for part. 



How the Thorax Changes its Capacity. Breathing, as 
shown above, is accomplished through changes in the thoracic space. 
This is increased by the elevation of the ribs and the depression of the 
diaphragm. The former process increases the transverse diameters; 
the latter the longitudinal diameter. The ribs are raised by the action 
of the muscles attached to them. The diaphragm, being naturally 
in an arched position, is depressed by the contraction of the muscles 
within it. As it lowers it pushes down the contents of the abdomen. 

Experiment. With five narrow strips of cardboard, one eight inches long 
and each of the others six inches, construct a figure to represent the thorax. Let 
the long strip serve as the spinal column and one of the short ones as the breast 
bone. Fasten the others between them for ribs. The fastenings, which must 
admit of motion, may be made by pushing pins through the strips where they 
join. 

Holding the piece representing the spinal column in a vertical position, 
raise and lower the piece representing the breast bone. When is the space be- 
tween the upright pieces the greatest ? Apply to the action of the ribs in increas- 
ing the thoracic cavity. 

The capacity of the thorax is diminished by lowering the ribs and 
elevating the diaphragm. Ordinarily the ribs are lowered, when the 
muscles that elevate them relax, by their own weight and by the elastic 



36 ELEMENTS OF PHYSIOLOGY. 

reaction of rbe surrounding parts. In forced expiration, however, 
special muscles are brought into play. The diaphragm is not raised 
through its own action, but is pushed up by the contents of the abdo- 
men. These, in turn, are pressed upward by the contraction of mus- 
cles in the abdominal walk. 

To Estimate the Quantity of Air Breathed. Experiment, (a) Fill a 
half gallon fruit jar even full of water, cover the top with a stiff piece of paper, 
and invert, without spilling, in a pan of water. Insert a tube under the jar 
and blow the air expelled from the lungs in ordinary breathing into the jar. 
Count the number of expirations required to fill the jar and then calculate the 
quantity breathed out during a single expiration. This equals the amount 
breathed in at an average inspiration, and is called the tidal air. 

(b) Fill and invert the jar as before. This time, after an ordinary inspira- 
tion, empty the lungs as completely as possible. (A second vessel should be 
ready to receive the excess of air in case the jar should prove too small.) This 
air, less the tidal air, is called the reserve air. 

The air that is left in the lungs after the forced expiration is called the 
residual air. In quantity it nearly equals the sum of the tidal and the reserve 
air. From the results obtained calculate the capacity of the lungs tested. (For 
the average individual the ordinary capacity of the lungs is equal to about one 
gallon. In forced inspiration the quantity is increased about one-third, by what 
is called the complemental air.) 

Hygiene of Respiratory Organs. The liability of the lungs 
to attack from such a dread disease as consumption, makes questions 
touching their hygiene of first importance. Consumption never at- 
tacks sound lung tissue, but always has its beginning at some weak or 
enfeebled part of the lungs, which has lost its "power of resistance.'' 
Xeither is consumption inherited as many suppose. Weak lung tissue, 
however, may be transmitted from parents to children and this ac- 
counts for the frequent appearance of consumption in the same family. 
Consumption, as well as the other respiratory affections, can in the 
majority of cases be prevented by an intelligent observation of well 
known laws of health. 

Respiratory Health Rules. 

1. Breathe through the nostrils. 

2. Maintain an erect position both in sitting and standing. 

3. Practice deep breathing sufficiently to insure the easy access 
of air to all parts of the lungs. 

T. Wear clothing loose enough around the chest and waist to 
allow perfect freedom in the respiratory movements. 



RESPIRATION. 37 

5. Never permit a cold to settle on the lungs. If it cannot be 
relieved by counter-irritation, a physician should be consulted. 

6. Take active exercise in the open air. Exercise which causes 
a notable increase in the respiratory acts is of especial value in 
strengthening the lungs. 

7. Avoid smoking and the use of alcoholic drinks. Tobacco 
smoke irritates the upper air passages, causing in some instances what 
is called "the smoker's sore throat," 

Ventilation. The health of the respiratory organs and of the 
entire body as well, demands the breathing of pure air. By pure air 
is meant that which contains the same proportion of oxygen as the 
general atmosphere. (How does breathing render air impure ?) Ven- 
tilation is the process of bringing pure air into a room, and of getting 
rid of the air which is unfit for breathing purposes. Since warm 
air is lighter than cold air, suitable openings in the walls of dwellings 
enable currents of air to pass between the rooms and the outside at- 
mosphere. Care must be taken, however, to prevent drafts and to 
avoid too great a loss of heat from the rooms. The plan of ventilating 
must be adapted to the construction of the building, plan of heating, 
and the general condition of the weather. No specific directions can 
be given. 

The general rules below may be followed with good results in 
ventilating rooms where the air is not heated before being brought in. 

1. Introduce air into the room through many small openings 
instead of a few large ones. 

2. Introduce the air at the warmest portions of the room. 

3. Provide openings both at the upper and lower parts of the 
room. 

4. If a wind is blowing ventilate principally from the sheltered 
side of the house. 

Suggested Topics for Further Study. 1. The nature and action of the 
respiratory muscles. 

2. Relation of the pressure of the atmosphere to the process of breathing. 

3. Relation of respiration to the activity of the body. Determine the num- 
ber of respirations per minute (a) during rest and (b) after vigorous exercise. 

4. General lung structure. Remove and study the lungs of a frog. Observe 
their general structure when inflated. (The terminal spaces, at the ends of 
the bronchial tubes, are similar in structure to the entire lung of the frog. ) The 
specimen may be dried, while inflated, and preserved for future study. 

5. The action of cilia. . Make a study of cilia as follows: (a) Expose the 



38 ELEMENTS OF PHYSIOLOGY. 

back part of the mouth and the gullet of a recently killed frog. Drop on the 
surface some small shavings of cork and watch for any movement. The cilia 
will move the particles backward toward the stomach, (b) Mount some small 
particles, cut or scraped from such a specimen, on a glass slide, in a very weak 
solution of salt in water, and examine under a microscope, first with a low 
and then a high power. In the slowly moving cilia it may be observed that the 
motion is quicker in one direction than in the other. 

6. Artificial respiration. Study in some larger work the methods of ap- 
plying artificial respiration. 

Summary. The lungs form a contrivance for bringing about an 
exchange of gases between the air and the blood. Their construction 
and operation are in harmony with the nature and the properties of the 
atmosphere which supplies the oxygen that enters the blood and re- 
ceives the gases that leave the blood. The exchange of gases takes 
place at the air-cells, or alveoli, where the air comes very near a large 
surface of blood. The air is brought into and expelled from the lungs 
through the action of the respiratory muscles which alternately in- 
crease and diminish the cavity of the thorax. 

Review Questions. 1. How does the air leaving the lungs differ in compo- 
sition from that entering them? 

2 Name the air passages in their order. 

3. Describe the air spaces at the terminations of the bronchial tubes. 

4. How are the air passages kept open and clean? 

5. Give three reasons for breathing through the nostrils. 

6. How is air brought into and expelled from the lungs ? 

7. Give functions of the diaphragm. 

8. If thirty cubic inches of air pass into the lungs at each inspiration and 
.05 of this is retained as oxygen, calculate the number of cubic feet of oxygen 
consumed each day, the number of inspirations being eighteen per minute. 

9. Find the weight of a day's supply of oxygen, as found in the above 
problem, allowing 1.3 ounces as the weight of a cubic foot. 

10. Make a study of the school room with reference to its hygienic ventila- 
tion. 

11. Give general directions for the care of the lungs. 



CHAPTER VI. 

THE PASSAGE OF OXYGEN THROUGH THE BODY. 

What is the nature of oxygen ? What is its purpose in the body 
and how does it serve this purpose ? How is it taken up and given 
off by the blood ? What becomes of it after being used ? These are 
questions touching the maintenance of life and deserve careful con- 
sideration. 

The Properties of Oxygen are readily learned by examining 
it in an undiluted form. For method of generating and collecting 
it see Appendix. Four large-mouthed bottles filled with the gas are 
needed in the following 

Experiments: 1. Examine a bottle of oxygen noting its lack of color. In- 
sert a small burning splinter in the upper part of the bottle and observe the 
change in the burning. Remove quickly and extinguish the name, leaving only 
a spark on the end of the splinter. Lower the spark into the oxygen and observe 
the result. Repeat untilthe oxygen in the bottle is exhausted. 

2. Hollow out the end of a short piece of crayon, fasten a wire holder to it, 
and fill the cavity with powdered sulphur. Ignite the sulphur in the flame of an 
alcohol lamp and lower it into a bottle of oxygen. Observe the change in the 
rate of burning, the color of the flame, and the material formed in the bottle by 
the burning. The gas remaining is sulphur dioxide and has been formed by the 
uniting of the sulphur and the oxygen. 

3. Bend a small loop on the end of a piece of picture wire. Heat the loop 
in a flame and insert in some powdered sulphur. Ignite the melted sulphur which 
adheres and insert it quickly in a bottle of oxygen. Observe the dark brittle 
material which is formed by the burning of the iron. It is a compound of oxygen 
and iron, similar to iron rust, and has been formed by their uniting. 

Oxygen is an element of intense affinity, or combining power, and, 
because of this fact, is able to unite with many other elements to 
form compounds. It may unite slowly, as in the rusting of iron, or 
rapidly as shown in the preceding experiments. Combustion, or 
burning, is but a chemical uniting of oxygen and certain substances, 
attended by light and heat. Oxygen is therefore described as the 

39 



40 ELEMENTS OF PHYSIOLOGY. 

supporter of combustion. It supports combustion, however, by the 
simple method of uniting with the substances which burn and which 
are called combustibles. The substances which are formed by the 
burning, called products of combustion, are compounds of oxygen and 
the combustibles. It is thus seen that oxygen in common with other 
elements appears in two forms : First, that in which it is m a free, 
or uncombined, condition — the form in which it appears in the at- 
mosphere. Second, that in which it is a part of compounds, as in the 
products of combustion. 

The general term for designating the uniting of oxygen with 
other substances is oxidation. This includes combustion as well as 
the unions which take place more slowly. 

The Passage of Oxygen Through the Blood is effected by 
means of its relations with the haemoglobin of the red corpuscles. The 
oxygen and the haemoglobin are able to unite if brought in contact 
where the oxygen pressure.* or tension, is greater than about half a 
pound to the square inch, but they will not unite, and they separate, 
if already united, where the oxygen pressure is less than half a pound. 
At the lungs the oxygen pressure is nearly three pounds to the square 
inch, but this diminishes in the arteries, becomes still less in the 
capillaries, and falls to zero in the cells. This enables the blood to 
flow constantly from a place of high to a place of low oxygen pressure, 
and, in so doing, to take up the oxygen at the lungs and release it at 
the tissues. 

The Purpose of Oxygen. In the cells the oxygen is con- 
stantly uniting with the hydrogen and carbon which form a large part 
of the protoplasm and the food substances. This action, similar in 
many respects to the combustion in a stove, is in effect a continuous 
chemical change, in nature an oxidation, that never ceases during life. 
Evidence of this action of oxygen is found in its continuous disap- 

* Dalton has shown that the ability of gases to dissolve in liquids varies with 
the pressure to which they are subjected. It is also true that pressure increases 
the tendency of a gas to unite chemically with a liquid or solid. Where two or 
more gases are mixed, as in the atmosphere, each exerts the same pressure that it 
would if it were alone and the pressure of the mixture is the sum of the partial 
pressures of the several gases. Since oxygen comprises about one-fifth of the at- 
mosphere, the pressure which it exerts is one-fifth of the total pressure or, at the 
sea level, about three pounds per square inch. (15 x 5.) This is the oxygen 
pressure of the atmosphere. The lack of oxygen pressure in the tissues of the 
body is due to its scarcity and this to its rapid consumption at the cells. 



THE PASSAGE OF OXYGEN THROUGH THE BODY. 41 

pearance as a free element in the body and in the appearance of prod- 
ucts of oxidation. 

The maintenance of a condition of continuous oxidation is the 
chief and, it may he, the only purpose of oxygen in the body.* As 
a result of the oxidations, energy is liberated (Chapter XI) and sub- 
stances are formed which are added to the protoplasm, either to take 
the place of other material or to enable it to grow. At the same time 
materials are produced which cannot be used in the body and which 
must be disposed of as waste. 

Oxygen and the Maintenance of Life. In the setting free 
of energy in the body and in the formation of materials which may 
be added to the protoplasm, conditions necessary to the maintenance 
of life are provided. Because of the close relation of oxygen to these 
processes, as well as the observed fact that the stoppage of the supply 
results in death, it is frequently called the supporter of life. The 
substances with which it unites are, however, just as necessary to the 
maintenance of life as is oxygen. The dependence of life upon them 
appears less marked than in the case of oxygen, because they are ac- 
cumulated, or stored up, in the body, while oxygen must be continually 
supplied from the atmosphere as it is needed. 

Passage of Oxygen from the Body. In the oxidation of 
materials at the cells, oxygen leaves its free state and becomes a part 
of the compounds which are the products of oxidation. With carbon 
it unites to form carbon dioxide (C0 2 ) ; with hydrogen it forms water 
(H 2 0) ; and with nitrogen, hydrogen, and carbon it forms urea 
(!N" g H 4 CO.). These substances pass through the blood to the organs 
of excretion where they are removed as waste. It is through their 
removal that the oxygen is passed from the body. Carbon dioxide, 
the most abundant of these compounds is thrown off at the lungs and 
has alreadv been shown to be present in respired air. (Experiment, 

P- 2 9-) 

* The idea has become largely prevalent that the purpose of oxygen is to 
burn up, or destroy, substances injurious to the body and, in this way, to act as a 
purifying agent. While it may do this to a limited extent, it is highly misleading 
to regard this as its chief purpose. In fact, the oxygen of the body serves a pur- 
pose quite similar to the oxygen which supports combustion outside of the body. 
The oxygen in the stove, by uniting with the carbon and hydrogen of the wood, 
causes the combustion. Instead of uniting only with impurities that may be 
present in the stove, it unites with the valuable fuel and instead of destroying 
waste products, it helps to form such waste products as ashes and carbon dioxide. 



42 ELEMEXTS OF PHYSIOLOGY. 

Carbon Dioxide is a compound of carbon and oxygen and is 
formed when these substances unite. Its chemical symbol C0 2 
indicates one part of carbon and two parts of oxygen. The test for 
carbon dioxide is lime-water, with which it unites to form carbonate 
of calcium. By the mixing of lime-water and carbou dioxide a pre- 
cipitate of calcium carbonate is formed, changing the clear lime-water 
to a milky white color. 

Experiments. 1. (a) Attach a piece of charcoal (carbon) no larger 
than the end of the thumb to a piece of wire. Ignite the charcoal and lower it 
into a vessel of oxygen. Observe its combustion. Let it remain until it ceases 
to burn. Xote that in burning, the piece of carbon has diminished in size and the 
oxygen has disappeared. Has anything been formed in their stead? 

(b) Remove the charcoal and add a small amount of lime-water. (See Ap- 
pendix.) Cover the bottle and bring the gas and lime-water in contact by shak- 
ing. Note the change in color of the lime-water. What does this indicate? 

2. Burn a splinter in a large vessel of air, keeping the top covered. Add 
lime-water and shake. Xote and account for the result. 

3. Place several pieces of limestone (marble) in a fruit or candy jar holding 
at least one-half gallon. Barely cover the limestone with water and then add 
hydrochloric acid until a gas is rapidly evolved. This gas is carbon dioxide. 

(a) Examine it to see if it possesses color. 

(b) Insert a burning splinter and note the result. 

(c) Blow a small soap bubble on the end of a tube and disengage it so that 
it floats on the gas in the jar. (A tube three-eighths of an inch in diameter is 
best for this purpose.) 

(d) Tip the jar over the mouth of the tumbler, as you would in pouring 
water, though not far enough to spill the acid. Then insert a burning splinter 
in the tumbler. Result? 

Carbon dioxide is a colorless gas which is heavier than air and 
does not support combustion. It finds its way into the atmosphere 
as the result of the oxidation of carbon which takes place in combus- 
tion, in the decay of animal and vegetable substances, and in the chem- 
ical changes which occur in the bodies of animals. 

Passage of Carbon Dioxide through the Blood. Part of 
the carbon dioxide in the blood is dissolved in the plasma and part of 
it is in loose combination with substances found in the plasma and 
corpuscles. Its ability to dissolve in liquids, and to enter into chem- 
ical combinations, as well, varies with the carbon dioxide tension or 
pressure, This is greatest at the cells, less in the blood, still less in 
the lungs, and practically nothing in the outside atmosphere. The 
conditions, it appears, are just the reverse of those relating to oxygen, 



TEE PASSAGE OF OXYGEN THBOUGE TEE BODY. 43 

and this accounts for its being taken up at the cells and given off at 
the lungs. 

Final Disposition of Carbon Dioxide. It is readily seen 
that, if the union of oxygen and carbon continually removes oxygen 
from the air and replaces it with carbon dioxide, the whole atmos- 
phere will become deficient in the one and have an excess of the other. 
This condition is prevented through the agency of vegetation. Plants 
absorb the carbon dioxide from the air, decompose it, build the carbon 
into compounds that become a part of the plant, and return the oxygen 
to the air. In doing this, they not only preserve the necessary pro- 
portion of oxygen and carbon dioxide in the atmosphere, but also put 
the carbon and the oxygen in such a condition that they may again 
unite. The process is carried on in the leaves of plants, but takes 
place only in the presence of sunlight. 

The form in which oxygen enters and leaves the body, as well as its trans- 
formation in passing, may be illustrated as follows : 

Into a glass tube, six inches in length, place several small lumps of charcoal. 
Fit in one end of this tube a second small glass tube which is bent at a right 
angle and made to pass through a close fitting stopper to the bottom of a small 
bottle. A second small tube is fitted in the stopper, but which terminates near 
the top of the bottle. The whole arrangement is now such that by sucking air 
from the top of the bottle it is made to enter the distant end of the tube contain- 
ing charcoal. Now fill the bottle one-third full of lime-water and heat the tube 
containing charcoal until it begins to glow. Suck the air through the tube and 
the bottle, observing what happens at both places. What are the proofs that the 
oxygen, in passing through the tube, unites with the carbon, forms carbon dioxide, 
and liberates energy? 

Summary. Oxygen, by uniting with the carbon and hydrogen 
of protoplasm and of food substances, maintains a condition of con- 
tinuous oxidation at the cells. It enters the body as a free, or un- 
combined, element and leaves it as a part of the compounds that it 
helps to form. The free oxygen is transported from the lungs to the 
cells by means of the haemoglobin of the red corpuscles, while the 
combined oxygen in carbon dioxide and other compounds is carried 
from the cells by the plasma. The limited supply of oxygen present 
in the body at any time makes necessary its continuous introduction 
into the body. 

Review Questions. 1. State the purpose of oxygen in the body. What 
properties enable it to fulfill this purpose ? 



44 ELEMENTS OF PHYSIOLOGY. 

2. How does the oxygen entering the body differ from the oxygen leaving 
the body? 

3. What is the necessity for the continuous introduction of oxygen into the 
body, while food is introduced at intervals? 

4. How are the red corpuscles able to take on and give off oxygen? How is 
the plasma able to take up carbon dioxide at the cells and give it off at the lungs ? 

5. If thirty cubic inches of air pass from the lungs at each expiration and 
four per cent of this is carbon dioxide, calculate the number of cubic feet of the 
gas produced in twenty-four hours, the number of respirations being eighteen per 
minute. 

6. What is the weight of this volume, if one cubic foot weighs 1.79 ounces": 

7. What portion of this weight is oxygen and what carbon, the ratio by 
weight of carbon to oxygen being twelve to thirty-two? 

8. What is the final disposition of the carbon dioxide in the atmosphere? 



CHAPTEK VII. 

FOODS. 

How the Chemical Changes in the Body Differ from 
those in a Stove. In the preceding chapter, the similarity 
between the chemical changes in the body and those in a stove was 
suggested. A closer investigation shows some important differences. 
The oxidations in the body, which are much slower than those in the 
stove, are never attended by the production of light and take place 
at a much lower temperature. Accurately speaking there is no com- 
bustion in the body. Another difference of perhaps greater impor- 
tance is the following: In the stove the action of the oxygen is lim- 
ited to the fuel, while in the body it unites with the cell protoplasm 
as well as with what corresponds to the fuel and is called food. In 
other words, the body itself is consumed by the oxidations. It is 
necessary, therefore, that both the protoplasm and the food be re- 
placed in the cells and this requires the rapid introduction of new 
materials into the body. 

Purposes of Food. Poods are substances that, on being taken 
into the normal body, assist in carrying on its work. This defini- 
tion properly includes oxygen, though the term is usually limited to 
substances introduced through the digestive organs. Poods serve at 
least three purposes: 1, They provide materials for rebuilding the 
tissues. 2. They supply the body with energy.* 3. They render 
indirect service which is neither that of rebuilding the tissues nor 
supplying energy, but which is necessary to both processes. 

Substances Suitable for Food. It is well known that not 
all substances which contain materials needed for rebuilding tissues 
can be used as food. It is also true that many substances which yield 
energy outside of the body, are unsuited to supplying energy within 



* Energy appears in the body chiefly as heat and as mechanical motion. ( See 
Chapter XL) 

45 



*6 ELEMENTS OF PHYSIOLOGY. 

the body. In general, materials to serve as food must conform to the 
following conditions : 

1. They must be capable of reduction to a liquid state, or to 
a finely divided condition, which makes it possible for them to be 
taken into the body and distributed by the blood to the cells. 

2. If they are to build tissue or yield energy they must be 
capable of oxidation. * that is. they must consist of compounds in which 
the union of the parts is weak enough to permit of their union with 
oxygen. 

3. Their properties must be such that they yield themselves 
readily to the body's method of taking up and appropriating new ma- 
terial and they must not injure the tissues. 

These conditions limit food substances to a comparatively small 
number of compounds which are obtained chiefly from the animal and 
vegetable kingdoms. 

Kinds of Food. The different classes of foods are shown by 
the following table: 



I. Mtrosenous substances 



Proteids. 

Albuminoids. 

Carbohydrates 



Xon-nitrosenous substances 



^ Oil. 
Common salt. 
3. Mineral salts J Phosphate of calcium. 



Sugar. 

Starch. 



C Solid fat. 
[ Fat 



Carbonate of calcium. 



•i. Water. 



While it is essential that foods supply all the chemical elements 
of the body, there is no simple food, nor class of foods, that contains the 
whole number. The nitrogenous foods contain carbon, hydrogen, oxy- 
gen and nitrogen. The non-nitrogenous contain carbon, hydrogen and 
oxygen. The mineral salts contain the other elements of the body. 

* These foods are readily oxidized outside of the body as shown by their ten- 
dency to decay and the ease with which they may be burned. An interesting ex- 
periment is to burn food substances such as sugar, starch, fat. etc., and determine 
their products of oxidation. 



FOODS. 4.7 

The Proteids form by far the larger and more important class 
of nitrogenous foods. Different varieties of proteids are represented 
by albumin found in the white of eggs, the lean of meat, and in the 
plasma of the blood ; by casein found in milk and cheese ; by gluten 
found in grains ; and by legumen in beans and peas. Since these com- 
pounds contain the four chief elements of the body they are made to 
serve the important purpose of rebuilding tissues. As they readily 
oxidize in the body they also supply energy. Their value as food is 
further increased by the fact that they are easily digested and in- 
troduced into the system. 

The Albuminoids form a small class of nitrogenous substances 
which differ from the proteids in being unable to rebuild tissue. The 
best known example is gelatine, a constituent of soup, obtained from 
bones and connective tissue by boiling. The albuminoids being ox- 
idizable in the body supply energy. 

Carbohydrates. The carbohydrate of greatest importance, 
as a food and also the one found in greatest abundance, is starch. 
All green plants form more or less starch and many of them store 
it in their leaves, seeds or roots. From these sources it is 
obtained as food. Glycogen, a substance closely resembling starch, is 
found in the bodies of a few animals, like the oyster, and is manu- 
factured to quite an extent by the liver. Glycogen is sometimes called 
animal starch. The sugars are derived from such plants as sugar- 
cane and beets, and from fruits. While there are several varieties 
of sugar, only two are present in any considerable quantity in our 
foods. These are sucrose, or cane-sugar, and glucose, or grape-sugar. 
The former is obtained in large quantities from sugar cane and beets 
while the latter occurs in ripe fruits and in honey and is also manufac- 
tured from starch. 

Composition of Foods. The composition of sucrose is represented by the 
chemical formula C12H22O11, that of glucose by C6H12O6, and that of starch by 
(C6Hio05)n. Butter, or glyceryl butrate, is C3H5(C4H:02)3 and another va- 
riety of fat is C3H5(Ci8H.3502)3. The exact composition of proteid compounds 
has never been determined. They are known, however, to be much more complex 
than the carbohydrates and fats. 

Purpose of Non-Nitrogenous Foods. Since these foods do 
not contain nitrogen, they are unable to supply that element to the 
protoplasm. For this reason they cannot be used by themselves in 
rebuilding any tissue except the adipose, and if taken alone they are 
unable to sustain life. They are, however, readily oxidized in the 



48 ELEMENTS OF PHYSIOLOGY. 

body and may be used in relatively large quantities in supplying 
energy, and this is their chief function. They also protect the nitrog- 
enous substances of the protoplasm from oxidation and, in this way, 
lessen the quantity of proteid that would otherwise have to be taken. 
They have a large energy value and their products of oxidation are 
simple and easily removed from the body. For the simple purpose of 
supplying energy they are superior to the proteids. 

Water finds its way into the body as a pure liquid, as a part of 
such mixtures as coffee, chocolate, and milk, and as a constituent of 
all our solid foods. (See table of foods, p. 50.) It is also formed in 
the body by the uniting of oxygen with the hydrogen. It passes through 
the body unchanged and is constantly being removed by all the organs 
of excretion. While water neither builds tissue nor liberates energy, 
it is as necessary to the maintenance of life as oxygen or proteids. It 
occurs in all the tissues and forms about two-thirds of the entire 
weight of the body. Its presence is necessary for the interchange of 
materials at the cells and for keeping the tissues soft and pliable. 
P. 27. ) As it enters the body it carries digested food substances with 
it and as it leaves, it is loaded with waste material. Its chief physi- 
ological work, which is that of a transporter of material, depends upon 
its ability to dissolve substances and to flow readily from place to place. 

The Mineral Salts are found in small quantities in the com- 
mon articles of diet and, as a rule, find their way into the body unno- 
ticed. They serve a variety of purposes. Phosphate and carbonate of 
calcium are important constituents of bone, and iron is a necessary 
part of the haemoglobin of the blood. Others play certain parts in the 
vital processes. Perhaps the mineral compound of greatest importance 
is sodium chloride,* or common salt. It is a natural constituent of 
most of our foods and is also added in the preparation of food for the 
table. When it is withheld from animals for a considerable length of 



* The recently advanced theory that mineral salts, by dissolving in water, 
separate into their atoms, or other molecular divisions, part of which are charged 
with positive electricity and part with negative electricity, has suggested several 
possible uses for sodium chloride and other mineral salts in the body. The 
sodium chloride in the tissues is in such concentration as to be practically all 
separated into its sodium and chlorine particles, or ions. Working in line with 
this theory, Dr. Loeb and his associates, at the University of Chicago, have shown 
that the sodium ions are necessary for the contraction of the muscles, including 
the muscles of the heart. There is also reason for believing that different ions 
may enter into temporary combination with food particles, and in this way play 
a role in the nutritive processes. 



FOODS. 49 

time they suffer intensely and finally die. It is necessary in the blood 
and lymph to keep their constituents in solution, and it is thought to 
play an important role in the reaction of protoplasm, especially that of 
muscle. It is constantly leaving the body as an excretory product 
and must be constantly supplied in small quantities in the food. 

Relative Quantities of the Different Foods. If the pro- 
teids are introduced into the body only in the proportion in which they 
are needed to rebuild tissue, and the energy of the body is obtained 
chiefly from tbe carbohydrates and the fats, the ratio of the proteids to 
the others has been found to be about one to three. That is, for every 
pound of proteid there will be consumed about three pounds of non- 
nitrogenous foods. This ratio, however, holds only during health and 
a condition of moderate exercise. During excessive exercise or in 
very cold weather there is an increase in the demand for energy food. 
On the other hand, a condition of convalescence, calls for an increase 
in the proportion of proteids. Allowance must also be made for con- 
stitutional differences in people which cause certain kinds of foods to 
be more easily digested and assimilated than others. 

Food Supply for the Table. The average daily meal should 
consist of both proteids and non-nitrogenous foods. The former can 
be obtained from a variety of food-stuffs such as lean meat, eggs, 
cheese, beans, peas, etc. The latter is supplied by potatoes, rice, but- 
ter, white bread, cereals, fat meat, etc. Fruit in some form should be a 
portion of each meal, as much for its tonic effect on the digestive organs 
as for what it yields in proteids or carbohydrates. Variety in the sup- 
ply of food for the table is an essential condition, but need not in- 
crease either the work or the expense of supplying food. Each single 
meal may and should be, simple in itself and still differ sufficiently 
from the meal preceding and the one following to give the required 
variety in the course of a day. 

Composition of Food-Stuffs. In a very few cases only do the 
different articles that comprise our daily food represent single pro- 
teids or carbohydrates, but most of them are mixtures in which some 
one food-substance predominates. The following table condensed from 
Atwater's "Foods: Nutritive Value and Cost," published by the U. S. 
Department of Agriculture, shows the percentage of proteids, fats, 
4 



50 



ELEMENTS OF PHYSIOLOGY. 



carbohydrates, water, and mineral salts in the edible portions of the 
more common substances taken as food: 



Food Materials. 


Water. 


Solids. 


Pro- 
teid. 


Fat. 


Carbo- 
hydrates. 


Mineral 
matter. 


Fuel 

value 

of one 

pound. 


Animal foods, edible portion. 
Beef : 


Per ct. 
63.9 
48.1 
60 
68.2 

68.8 

58.6 
61.8 
49.3 

50.3 
41.5 
12.1 

41.5 

62.4 

72.2 

66.2 

73. 8 

87 

10.5 

11 

30.2 
41.3 

82.6 
63.6 
87.1 

12.5 
13.1 
13.1 
14.6 

7.6 
15 

12.4 
12.3 
12.6 
78.9 
71.1 
89.4 
87.6 
78. 2 
78.1 
81.3 
96 

91.9 
83.2 

2 
24.6 
32.3 

8.3 


Per ct. 
36.1 
51.9 
40 
31.8 

31.2 

41.4 
38.2 

50.7 

49.7 
58.5 

87.9 

58.8 

37.6 

27.8 

33.8 

26.2 

13 

89 

89.5 

69.8 
58.7 

17.4 
86.4 
12.9 

87.5 

86.9 

86.9 

85.4 

92.4 

85 

87.6 

87.7 

87.4 

21.1 

28.9 

10.6 

12.4 

12.8 

21.9 

18.7 

4 

8.1 
16.8 
98 
75.4 


Per ct. 
19.5 
15.4 
18.5 
20.5 

20.2 

18.1 
18.3 
15 

16 

16.7 
.9 

13.8 
18.8 
24.4 
23.9 
14.9 

3.6 

1 
.6 

28.3 
38.4 

15.8 
21.6 
6 

11 

11.7 
6.7 
6.9 

15.1 
9.2 
7.4 

26.7 

23.1 
2.1 
1.5 
1.2 
1.4 
2.2 
4.4 
2.8 
.8 
2.1 
.2 


Per ct. 
15.6 
35.6 
20 5 
10.1 

9.8 

22.4 

19 

35 

32.8 
39.1 

82.8 

42.8 
15.8 

2 

8.7 
10.5 

4 
85 
85 

35.5 

6.8 

.4 
13.4 
1.2 

1.1 

1.7 

.8 

1.4 

7.1 

3.8 

.4 

1.7 

2 

.1 

.4 

.2 

.3 

.4 

.6 

1.1 

.4 

.3 

.4 


Per ct. 


Per ct. 
1 

.9 
1 
1.2 

1.2 

.9 
.9 

.9 
2.7 
4.2 

2.2 
3 

1.4 
1.2 

.8 
.7 
.3 
.3 

4.2 

4.6 

1.2 
1.4 
2 

.5 

1.8 

l" 

2 

1.4 
.4 

2.9 

3.1 

1 

1 

1 
.6 
.8 
.9 
.6 
.3 

1.1 
.3 
.2 

2.3 
.9 

2.4 


Calories 

1,020 

1,790 

1,210 

805 


Rib 


Sirloin 

Round 


Veal : 




790 


Mutton: 

Shoulder 


1,280 


Leg 




1,140 
1,755 


Loin 


Pork: 

Shoulder roast, fresh 




1,680 
1,960 
3,510 

2,065 






Fat. salted 




Sausage : 

Pork 








1,015 
540 


Chicken 




Turkey 

Eggs 

Milk 


"iW 

.5 
.4 

1.8 
8.9 


810 
721 
325 


Butter 

Oleomargarine 

Cheese: 

Full cream 


3,615 
3,605 

2.070 
1,165 


Fish: 

Codfish 


310 


Salmon 


"3.7 

74.9 
71.7 
78.7 
76.1 
68.2 
70.6 
79.4 
56.4 
59.2 
17.9 
26 

8.2 
10.1 

9.4 
16 
13.2 

2.5 

5.5 
15.9 
97.8 
73 1 
56.3 
68.7 


965 
2:30 


Vegetable foods. 
Wheat flour 


1,645 

1,625 


Rye flour 


1.625 
1.605 


Oatmeal 


1,850 
1,645 


Rice 


1.6:30 


Peas 

Beans 


1,565 

1,615 

375 


Sweet potatoes 

Turnips 

Onions. 

String beans. 


530 
185 
225 
235 
405 


Green corn 

Tomatoes 


345 
80 

155 


Apples 

Sugar, granulated 


315 
1,820 






1,360 


White bread (wheat 

Boston crackers j 


8.8 
10.7 i 


1.7 
9.9 


1,280 
1,895 



The Effects of a One-Sided Diet. If an insufficient amount 
of proteid is supplied to the body, the tissues are improperly nourished 
and one is unable to exert his normal strength. On the other hand, if 



FOODS. 51 

proteids are eaten in excess of the needs of the body, extra work is 
thrown on the organs of excretion. Sometimes they are unable to 
remove all the products of proteid oxidation and disorders like gout 
and certain forms of rheumatism result. 

Where it is desirable to supply the table at as small a cost as pos- 
sible, the vegetable proteids may be used to good advantage. (See 
table of foods.) While some of these are not so readily digested as 
meats, they are otherwise just as satisfactory from a hygienic stand- 
point. 

Is Alcohol Suitable for Food? Many people in this and 
other countries drink in different beverages, such as whiskey, wine, 
beer, etc., a variable amount of alcohol. This substance has a tem- 
porary stimulating, or exciting, effect on the nervous system and the 
claim has been made that it may serve as food. .Recently it has been 
shown that when alcohol is greatly diluted and introduced into the 
body in small quantities it is nearly all oxidized and yields energy as 
does fat or sugar. Still it cannot be said that all substances that can 
be oxidized are suitable for food. They may possess additional prop- 
erties which produce harmful effects and this is the case with alcohol. 
When used in large quantities it injures nearly all the tissues in the 
body and when taken habitually, even in small doses, It leads to the 
formation of the "alcohol habit," which is now recognized as a disease. 

While the direct effect of alcohol on the various tissues is not understood, 
there are certain facts that throw light upon this point. One of these is the action 
of alcohol upon the proteids of protoplasm and may be illustrated by the follow- 
ing simple 

Experiment. Place some of the white of a raw egg in a glass vessel and 
cover it with a small amount of alcohol. As the albumin hardens^ or coagulates, 
observe that the quantity of clear liquid increases. This is due to the withdrawal 
of water from the albumin by the alcohol. If, instead of pure albumin, some 
tissue of the animal body, such as a muscle or a part of the liver, were to be used, 
a similar effect would be produced. 

Of course alcohol in the living body is soon diluted and does not produce such 
marked results. If it did, death would quickly result. However, when the actual 
changes that do occur in the body by the prolonged use of alcohol, are considered, 
it seems probable that a similar action may take place in the living tissues, 
though to a limited degree. (P. 139.) 

Instead of being classed as a food, alcohol more properly belongs 
to a large list of substances which act strongly upon the body to bring 



52 ELEMENTS OF PHYSIOLOGY. 

about abnormal and unusual effects. These substances are known by 
the general name of 

Drugs. Drugs embrace a very large number of substances, 
many of which are used as medicines, but the majority of which, if 
taken in sufficient quantity, act as poisons. The legitimate and benefi- 
cial use of drugs in any individual case can only be determined by a 
physician. Science sanctions their use only in cases of emergency, 
where the injurious effects of disease must be counteracted or where 
the normal activity of the various organs fails temporarily to meet the 
demands made upon them. Not only are they of no value in health 
but their use is attended with great danger. 

Summary. Materials called foods are introduced into the body 
for the purpose of rebuilding tissue, supplying energy, and aiding 
indirectly in the work of the body. The properties of these sub- 
stances must be such as to adapt them to the body's method of handling 
materials and they must injure none of the tissues. Only a few classes 
of substances, viz., proteids, carbohydrates, fats, and some mineral 
compounds have all the qualities of foods and are suitable for introduc- 
tion into the body. Substances known as drugs, which may be used as 
medicines in disease, should be avoided in health. 

Review Questions. 1. Give two differences between the chemical changes in 
the body and those in a stove. 

2. What purposes are served in the body by foods ? 

3. Give the necessary qualities of substances that are suitable for food. 

4. Wood and coal contain energy ; why can not they be used as food ? 

5. Why are non-nitrogenous foods taken alone, unsuited for rebuilding tis- 
sue? 

6. W T hat advantages have the non-nitrogenous over the nitrogenous foods in 
furnishing energy? 

7. Show that life can not be carried on without water. 

8. Consulting the table on page 50, select four foods which, if eaten at a 
single meal, will furnish the correct proportion of tissue building and energy 
material. 

9. What are the proofs that alcohol is not a food ? 



CHAPTEK VIII. 

THE ABDOMEN AND ITS CONTENTS. 

The entrance of food into the body is effected through the organs 
of digestion. These, for the most part, occupy the space below the 
thorax and within the abdomen, called the abdominal cavity. This is 
a large cavity, holding other organs than the digestive, and ranks in 
importance with the thoracic cavity. Its general study affords a good 
introduction to the nature and purpose of the organs that it contains. 

Dissection of the Abdomen. Tor individual study, or for a 
small class, a half-grown cat is perhaps the best specimen available. 
It should be killed with chloroform and then stretched, face upward, 
on a board, the feet being secured to hold it in place. 

The teacher should make a preliminary examination of the abdo- 
men to see that it is in a fit condition for class study. If the bladder 
is unnaturally distended, its contents may be forced out by slight pres- 
sure. 

The following materials will be needed during the dissection and 
should be kept near at hand: A sharp knife with a good point, a 
pair of heavy scissors, a vessel of water, some cotton batting or a 
sponge, and some fine cord. 

During the dissection the specimen should be kept as clean as 
possible. The escaping blood should be mopped up with cotton or a 
damp sponge. (See Appendix.) 

Order of Observations. 1. Cut through the abdominal wall in the center of 
the triangular space where the ribs converge. From here cut a slit downward to 
the lower portion of the abdomen and sideward, each way, as far as convenient. 
Tack the loosened abdominal walls to the board and proceed to study the exposed 
parts. Observe the muscles in the abdominal walls and the fold of peritoneum 
which forms an apron-like covering over the intestines. 

2. Observe the position of the stomach, intestines, liver, and spleen, and 
then, by pushing the intestines to one side, find the kidneys and the bladder. 

3. Trace out the continuity of the food canal. Find the oesophagus, the 
tube from the mouth, where it penetrates the diaphragm and joins the stomach. 
Find next the union of the stomach with the small intestine. Then by care- 

53 



51 ELEMENTS OF PHYSIOLOGY. 

fully following the coils of the small intestine, discover its union with the large 
intestine. 

4. Study the liver with reference to location, size, shape, and color. On the 
underside, find the gall bladder from which a small tube leads to the small intes- 
tine. Observe the portal vein as it passes into the liver. As the liver is sur- 
charged with blood, care must be taken to prevent cutting it, or its connecting 
blood vessels. 

5. Within the first coil of the small intestine as it leaves the stomach find 
the pancreas. Note its color, size, and branches. Find where it connects with the 
small intestine. 

6. Beginning at the cut portion of the abdominal wall, lift the thin lining, 
called the peritoneum, and carefully follow it toward the back and central por- 
tion of the abdomen. Observe whether it extends back or in front of the kidneys, 
the aorta, and the vena cava. Find where the right and left portions unite to form 
a rather heavy double membrane, the mesentery, which passes from the poste- 
rior abdominal wall and surrounds and holds in place the large and small intes- 
tines. 

7. Tie the canal tightly in two places, half an inch apart, above the stomach 
and cut it in two between these places. Likewise tie and cut the rectum. The 
stomach and intestines may now be removed from the abdominal cavity and 
studied to better advantage. Examine the mesentery and its connection with the 
intestines. Notice the divisions of the portal vein and the lacteals passing 
through it. Sketch a coil of the intestines and the mesentery attached to it. 

8. Find in the center of the coils of the small intestine an elongated, gland- 
like body. This is the beginning of the thoracic duct and is called the receptacle 
of the chyle. From this the thoracic duct rapidly narrows until it becomes diffi- 
cult to trace in a small animal. 

9. Cut away about two inches of small intestine from the remainder. Split 
it open for a part of its length and wash out its contents. Observe its coats. 
Place in water and examine the mucous membrane with a lens to find the villi. 

10. Study the connection of the small intestine with the large; split it open 
at this place, wash out contents, and examine the ileo-coecal valve. 

11. Observe the size, shape, and position of the kidneys. Do they lie in 
front or back of the peritoneum? Do they lie exactly opposite each other? 

12. Note the connection of each kidney with the aorta and inferior vena 
cava by the renal artery and renal vein. Find a slender tube, the ureter, running 
from each kidney to the bladder. Do the ureters connect with the top or base of 
the bladder? Show by a sketch the connection of the kidneys with the large 
blood vessels and the bladder. 

The Abdominal Cavity lies immediately below the cavity of 
the thorax and is separated from it by the diaphragm. Its surround- 
ing walls are continuous with those of the thorax, but are less resisting 
and admit of greater freedom of motion. The spinal column and 
muscles of the loins form a heavy, supporting structure at the back, 
while the sides and front are made up mainly of connective tissue and 



THE ABDOMEN AND ITS CONTENTS. f>5 

sheets of muscle. The cavity terminates below in the hollowed-out 
portion of the pelvic bones. These join firmly with the spinal column 
behind and provide suitable projections for the attachment of the mus- 
cular walls in the front and at the sides. 

Location of Abdominal Organs. The general form and ar- 
rangement of the abdominal organs in man are similar to that of the 
animal dissected. The space immediately below the diaphragm is 
occupied by the liver and stomach, the liver being chiefly on the right 
side and the stomach on the left, The central portion of the cavity is 
occupied by the small intestine. This is so coiled that a narrow 
space is left between it and the right and left abdominal walls and also 
between it and the stomach. The large intestine occupies this space 
and, in so doing, almost completely encircles the coil of small intes- 
tine. To the left and a little below the stomach is the spleen. The 
kidneys lie against the posterior abdominal wall, on either side, 
slightly above the middle, while the bladder occupies the central lower 
portion of the cavity. 

The Peritoneum, the lining membrane of the abdominal cavity, 
has the same general arrangement as the pleura in the cavity of the 

thorax. It forms a continuous lining 
for the walls of the cavity, including 
^^^^S^\ the diaphragm above and the pelvic 

ip CT) 2 \\\ basin below, and forms an outside cov- 

( | 4 d£> 5 I | ering to all the organs in the cavity 

Y^S^^^^^y J except the kidneys and the bladder. 
X ^ *^r ^ y It is the most extensive serous mem- 

brane of the body. The part extend- 

Fig.16. Relations of the peritoneum. mg from the Spinal Column TO the 

neys F °5 d *™^^S^. b*£\ large and small intestines, is called 
neTm^sTnd'caS^t^Tot^d ime perit °- the mesentery. It appears as a thin, 

transparent membrane, containing 
blood and lymph vessels, and surrounds and supports the intestines as 
an arm is supported in a sling. Friction is prevented in the move- 
ments of the abdominal organs by the peritoneal fluid which is se- 
creted in small quantities. 'Fig. 16. 

The Abdominal Walls, except at the back, are rather thin and 
flexible and permit freedom of motion in the bending and twisting of 
the trunk. This is the more necessary at this part of the body since 
the arrangement of the ribs is such that the upper part of the trunk is 



56 ELEMEXTS OF PHYSIOLOGY. 

more or less rigid. The muscles in the walls cause various move- 
ments of the trunk while the long muscular band which extends ver- 
tically over the front of the abdomen, called the abdominis rectus, is 
able by contraction to diminish the size of the abdominal cavity. The 
pressure which it is able to exert may be transmitted to the underside 
of the diaphragm, to aid in expelling the air from the lungs. (P. 36.) 

Hygiene. TThile the clothing around the waist may be snug 
and close-fitting, it should never be of a nature to interfere with the 
freedom of the abdominal movements. Tight lacing, if long contin- 
ued, weakens the abdominal walls, breaks down the natural thoracic 
arch, and deforms and displaces such important organs as the liver 
and the stomach. The imaginary gain in beauty of form, by such 
practice, is more than counterbalanced by loss of grace and ease of 
motion, to say nothing of the liability of injury to the health. 

Summary, The abdomen provides a suitable cavity for holding 
the digestive and other important organs. Its walls are muscular 
and pliable, yield readily in the different movements of the trunk, and 
render indirect aid in the process of respiration. 

Review Questions. 1. "What cavities are found in the trunk? Xame the 
important organs in each. 

2. Compare the pleura and the peritoneum with reference to structure, gen- 
eral arrangement, and function. 

3. Give the function of the abdominal muscles and the diaphragm. 

4. How are the abdominal walls held in position? 

5. What changes in the abdomen take place during respiration? Why are 
these changes necessary? 

6. Draw a curved line to represent the general shape of the abdominal cav- 
ity and indicate within it the position of the stomach, liver, spleen, kidneys, and 
bladder. 



CHAPTEK IX. 

DIGESTION. 

Digestion is the process by which food materials are prepared 
for the blood. Since only liquids and dialyzable materials can enter 
the blood vessels, digestion mnst consist, to a. large extent in chang- 
ing solids into liquids and in converting non-dialyzable into dialyza- 
ble* substances. The process is partly mechanical and partly chemical 
and may be imitated to some extent by dissolving substances in liquids. 

Experiment. To a tumbler two-thirds full of water add a little salt. Stir 
and observe the effect of the water on the salt. Taste the solution to see that 
the salt has not been changed chemically. Now add a small bit' of lime and stir 
as before. Observe that while the lime may be separated into smaller pieces it 
does not dissolve. Now add some hydrochloric acid and stir as before, noting 
the result. 

In this experiment we are concerned with ( 1 ) water which is already a 
liquid, (2) salt which becomes a liquid by dissolving in water, (3) lime, or cal- 
cium hydroxide, which is practically insoluble in water but dissolves when hy- 
drochloric acid is added. The acid simply changes the insoluble calcium hydrox- 
ide into soluble calcium chloride which the water then dissolves. (4) Finally 
we note that a vessel, or container, is used to hold the materials concerned in the 
experiment. 

In the digestion of the food similar conditions are provided by 
the organs concerned. 

Digestibility of Foods. With reference to the changes they 
undergo during digestion, foods may be divided into three classes : 

1. Substances already in the liquid state. Water is the chief 
substance belonging to this class. Oils used for food and milk are 
exceptions. 

2. Foods soluble in water. This class includes several mineral 
substances and grape sugar. These require simply to be dissolved. 

* Dialyzable materials are those that can pass, when in solution, through 
animal membranes. (See experiment, page 27.) 

57 



58 



ELEMEXTS OF PHYSIOLOGY. 



3. Foods that are insoluble in water. The greater number of 
the solid foods, including proteids, starch, and fats, belong to this class. 
Their digestion consists in changing them into substances that are 
soluble in water. 

The Organs of Digestion are of three kinds: 1. Those 
for crushing and grinding the food. 2. Glands that secrete liquids 
which act upon the food to change it chemically and dissolve it. 3. 
Cavities in which the different processes of digestion take place and 
tubes connecting them. 

The different cavities and the tubes are connected to form one 
continuous passageway which, beginning at the mouth and extending 
entirely through the body, forms the alimentary canal. The parts of 
this canal and the glands which aid in digestion are shown by the 
following table: 



Mouth 
Pharynx 
( Parts of <( Oesophagus 
Alimentary | Stomaeh 



Digestive 
Organs 



Canal 



Digestive 
(^ Glands. . . 



{ Salivary . . 
| Gastric 
. { Liver 
| Pancreas 
^ Intestinal 



f Duodenum 
Small. < Jejunum 
1 Ileum 



^Intestines. . . { 



{ Coecum and vermiform appendix 
f Ascending 



^ Large. <J Colon. . . 

^Rectum 
r Parotid 
< Submaxillary 
[ Sublingual 



Transverse 
) Descending 
^ Sigmoid flexure 



The Alimentary Canal varies in length in different individ- 
uals from 25 to 30 feet. Its parts present such differences as adapt 
them to their particular work although a general similarity of struc- 
ture prevails. Its walls, except at the mouth, are distinct from the 
surrounding tissues and consist, for the most part, of separate layers 
or coats, as follows: 1. The first coat, or lining, consists of mucous 
membrane and is named from a liquid which it secretes, called mucus. 
This membrane is not limited to the alimentary canal but lines all 
the cavities of the body to which air has access. Since it is continu- 
ous with the skin, where these cavities open at the surface of the 
body, it is sometimes called the "inner skin." It resembles the skin 
in structure, being made up of two layers — a thick under-layer which 



DIGESTION. 



59 



contains blood vessels, nerves and glands, and a thin surface layer 
of epithelial cells. 

2. The second, or middle, coat is muscular and forms a con- 
tinuous layer throughout the canal, except at the mouth. Here its 

place is taken by the strong 
muscles of mastication which 
are separate and distinct from 
each other. As a rule this 
muscle belongs to the non- 
striated, or involuntary, type 
and consists of two layers that 
surround the canal as sheets 
or bands. In the inner layer 
the fibers encircle the canal, 
but in the outer layer they are 
arranged longitudinally. 




3. The third, or outer, 
coat surrounds and is limited 
to those portions of the canal 
that occupy the cavity of the 
abdomen. This coat is a con- 
tinuation of the lining mem- 
brane of the cavity, called the 
peritoneum. (P. 55.) 

Another coat called the 
submucous which lies between 
the mucous and the muscular 
is frequently described. 

The Digestive Glands, 
sometimes described as acces- 
sory organs of digestion, are 
either situated in the mucous 
membrane of the canal or are 
located at convenient places and connect with the canal by tubes, 
called ducts. They manufacture their secretions from materials which 
they derive from the blood and empty them into the canal where they 
can act on the food. 

The Digestive Processes. Digestion is accomplished by acting 
upon the food in different ways, as it is passed along the canal, with 



Fig. 17. Diagram of the digestive system. 1. 
Mouth. 2. Soft palate. 3. Pharynx. 4. Parotid 
gland. 5. Sublingual gland. 6. Sub-maxillary gland. 
7. Oesophagus. 8. Stomach. 9. Pancreas. 10. Ver- 
miform appendix. 11. Coecum. 12. Ascending colon. 
13. Transverse colon. 14. Descending colon. 15. 
Sigmoid flexure. 16. Rectum. 17. Ileo-cOecal valve. 

The position and connections, not the relative 
length, of the small intestine are shown in the figure. 



60 ELEMENTS OF PHYSIOLOGY. 

the final purpose of reducing it to a liquid and dialyzable condition. 
Several distinct processes are necessary and they occur in such an 
order that those preceding are preparatory to those that follow. These 
processes are mastication, insalivation, deglutition, stomach digestion, 
and intestinal digestion and they take place in the order named. As 
the different materials become liquified they are transferred to the 
blood by a special process known as absorption. Substances not re- 
ducible to the liquid state pass on through the canal as waste. 

The Mouth is an oval-shaped cavity situated at the very begin- 
ning of the canal. It is surrounded by the lips in front, the cheeks 
on the sides, the soft palate behind, the hard palate above, and the ( 
tissues of the lower jaw below. The mucous membrane lining the 
mouth is soft and smooth being covered with flat epithelial cells. The 
external opening of the mouth is guarded by the lips while the soft 
palate forms a movable partition between the mouth and the pharynx. 
In a condition of repose the mouth space is all taken up by the tongue 
and the teeth ; but the cavity may be increased and room provided for 
food by depressing the lower jaw. The mouth by its construction is 
adapted to carrying on the processes of 

Mastication and Insalivation. Mastication is the process 
by which solid food is reduced, by the cutting and grinding action of 
the teeth, to a finely divided condition. Insalivation is the process of 
mixing the food with saliva. Both processes take place at the same 
time and are accomplished, in part, by the same agencies. The saliva 
dissolves the soluble portions of the food, softens and lubricates por- 
tions that it cannot dissolve, and acts chemically upon the starch, 
changing it into a form of sugar. The main purpose of both mastica- 
tion and insalivation is to prepare the food for the processes that are 
to follow. 

Experiments. 1. Fill two tumblers each half full of water. Into one place 
a lump of rock salt. Into the other place an equal amount of salt that has been 
pulverized. Which dissolves first? Why? 

2. Hold in the mouth for one or two minutes a small piece of red litmus 
paper. Note and account for change in color. (The turning of red litmus blue 
indicates an alkaline condition of the mouth.) 

3. Prepare starch paste by mixing one-half of a teaspoonful of starch in half 
a pint of cold water and bringing it to a boil. Place some of this in a test tube 
and thin it by adding more water. Then add a small drop of a solution made by 
dissolving iodine in alcohol. It should turn a deep blue color. This is the test 
for starch. Now collect from the mouth, in a clean test tube, two or three tea- 



DIGESTION. 61 

spoonfuls of saliva. Add portions of this to small amounts of fresh starch solu- 
tion in two test tubes. Let the tubes stand for five or ten minutes surrounded by- 
water, having about the temperature of the body. Test for changes that have 
occurred as follows: 

(a) To one tube add a little of the iodine solution. If it does not turn blue, 
it shows that the starch has been changed into something else by the saliva, (b) 
To the other tube, add a few drops each of a solution of potassium hydroxide and 
of copper sulphate and boil the mixture. If it turns an orange red color, the 
presence of sugar is proven. 

4. Hold a little starch in the mouth until it is completely dissolved and ob- 
serve that it gradually gives a sweetish taste. 

The chemical action of saliva is due to an active agent that it 
contains, called ptyalin, This acts best in the liquids that are slightly 
alkaline. 

Accessory Organs of the Mouth. The work of mastication 
and insalivation is accomplished through organs situated within and 
around the cavity of the mouth. These comprise : 

1. The teeth, which are set in two rows, one immediately over 
the other, in the upper and lower jaws, with their hardened surfaces 
facing. In reducing the food the lower jaw moves against the upper. 
The upper and lower front teeth, which are flat and chisel shaped, do 
not meet squarely, but their edges glide over each other, like the 
blades of scissors, a condition that adapts them to cutting off and 
separating portions of food. The back teeth are broad and irregular 
and are adapted to crushing and grinding the food. 

2. The tongue. This is a muscular organ whose fibers extend 
in several directions. This accounts for the great variety of move- 
ments which it is able to perform. Its chief work during mastica- 
tion is to transfer the food from one part of the mouth to another and, 
with the aid of the cheeks, to keep the food between the rows of teeth. 
But it has functions in addition to these and is, altogether, a most use- 
ful organ. 

3. The muscles of mastication, These are attached to the lower 
jaw and bring about its different movements. 

4. The salivary glands, which are situated in the tissues sur- 
rounding the mouth and communicate with it by means of ducts. 
These are six in number and are arranged in three pairs. The largest, 
called the parotid glands, lie, one on each side, in front of and below 
the ear. The next in size, the submaxillary, are located, one on each 
side, just below and in front of the triangular bend in the lower jaw. 
The smallest, the sublingual glands, are situated in the floor of the 
mouth, one on either side of the base of the tongue. 



62 ELEMENTS OF PHYSIOLOGY. 

(For more complete descriptions of the accessory organs of the mouth, the 
student is referred to some work on anatomy.) 

Deglutition, or swallowing, is the process by which the food is 
transferred from the mouth to the stomach. While it is not, strictly 
speaking, a digestive process, it is nevertheless necessary to the further 
digestion of the food. The chief organs concerned in deglutition are 
the tongue, the j)harynx, and the oesophagus. 

The Pharynx is a rounded sac-like body lying immediately back 
of the nostrils, mouth, and larnyx. It is somewhat funnel-shaped 
and extends from the under portion of the skull to where it joins the 
oesophagus. It has a length of about four and one-half inches and 
communicates with other parts of the body by seven separate openings. 
One of these is with the mouth, one with the oesophagus, one with the 
larynx, one with each of the nostrils and one with each of the middle 
ears. (Fig. 11, p. 31.) The pharynx is the part of the food canal 
that is crossed by the air passage and its upper portion properly be- 
longs to the system of air tubes. Within the walls of the pharynx 
is a series of over-lapping muscles which, by their contractions, draw 
its sides together and diminish the cavity. 

The Oesophagus, or gullet, is a tube eight or nine inches in 
length that connects the pharynx with the stomach. It lies for the 
greater part of its length in the thoracic cavity. It consists chiefly 
of a mucous lining surrounded by a heavy coat of muscle. 

Steps in Deglutition. 1. By the contraction of the cheek mus- 
cles, the food ball, or bolus, is pressed into the center of the mouth 
and upon the upper surface of the tongue. Then the tongue, by an 
upward and backward movement, pushes the food under the soft palate 
and into the pharynx. 

2. As the food passes into the pharynx, the soft palate is 
pushed backward and upward, closing the opening of the- pharynx 
above, while the pressure of the food on the epiglottis (p. 31) causes 
that body to close the opening into the larynx. In this way all com- 
munication between the food and air passage is temporarily closed. 
The upper muscles of the pharynx now contract upon the food, forcing 
it downward, and into the oesophagus. 

3. In the oesophagus the food is forced along by the successive 
contractions of the muscles above until the stomach is reached. 



DIGESTION. 63 

The Stomach is the largest dilatation of the alimentary canal. 
It is situated in the abdominal cavity, immediately below the dia- 
phragm, with the greater portion on the left side. It connects with the 
oesophagus at the upper, or cardiac, end and with the small intestine at 
its lower, or pyloric, extremity. It varies greatly in size in different 
individuals being on an average from ten to twelve inches at its 
greatest length, four to five inches at its greatest width, and holding 
when full, from three to five pints. It has the coats common to all 
parts of the canal, but with such modifications as adapt it to its special 
work. The muscular coat consists of three separate layers, which are 
named, from the direction of their fibers, the circular layer, the longi- 
tudinal layer, and the oblique layer. The circular layer becomes quite 
thick at the pyloric orifice, forming a distinct band which serves as a 
valve. 

The mucous membrane is thick and highly developed, containing 
great numbers of small granular bodies known as the gastric glands. 
These are of two general kinds and secrete in large quantities a liquid, 
called gastric juice. When the stomach is only partly filled, the 
mucous membrane is thrown into folds w 7 hich extend in a longitudi- 
nal direction. These disappear, however, when the walls of the 
stomach are distended with food. 

Stomach Digestion is largely a chemical process and is due to 
the action of the gastric juice. This is a thin, colorless liquid wdiich 
is composed chiefly of water. But dissolved in the water are several 
mineral salts and three active agents — hydrochloric acid, pepsin, and 
rennin. The chief action of the gastric juice is upon the proteids. 
These substances, being insoluble in water, are changed into two 
soluble substances, known as proteoses and peptones. The chief agent 
in bringing about this change is the pepsin which acts as an enzyme, 
or ferment. (Chap. 10.) The pepsin, however, is able to act only 
in an acid medium — a condition furnished by the hydrochloric acid. 

Experiment. After washing out the stomach of a recently killed pig, scrape 
off the mucous coat and mince it fine. Mix with some dilute hydrochloric acid 
(two per cent solution) and keep for a few hours in a warm place. Strain off 
the liquid. It will digest proteids, like normal gastric juice, although it contains 
impurities and decomposes on standing. To such a liquid add some boiled white 
of egg, finely minced, or some shreds of fibrin obtained from coagulated blood. 
Keep in a warm place for an hour or so and note the results. 

An artificial gastric juice which also gives good results in this experiment, 



6± ELEMENTS OF PHYSIOLOGY. 

may be prepared by adding scale pepsin, obtained from a drug store, to a two 
per cent solution of hydrochloric acid. 

The digestion of the starch which began in the month is checked 
in the stomach. This is because the ptyalin of the saliva, does not act 
in an acid medium. While there is no appreciable action on the fat 
itself, the proteid membranes that inclose the fat particles, are dis- 
solved away and the particles of fat are set free. 

The muscular layers, by alternately contracting and relaxing, 
mix the food with the gastric juice. The muscular band at the pyloric 
orifice remains contracted, keeping the opening into the small intes- 
tine closed, except at intervals, when it relaxes and allows materials 
to be forced from the stomach. 

In addition to carrying on a process of digestion, the stomach also 
serves as a necessary receptacle, similar in purpose to the hopper of 
certain machines, in which the food may be accumulated and from 
which it is gradually passed into the small intestine. 

The Small Intestine is a coiled tube, about twenty-two feet in 
length, which occupies the central and lower part of the abdominal 
cavity. At its upper extremity it connects with the pyloric end of the 
stomach and at its lower end it joins the large intestine. It averages 
a little over an inch in diameter and gradually diminishes in size from 
the stomach to the large intestine. The first eight or ten inches form 
a short curve that is separated from the main coil and is called the 
duodenum. The upper two-fifths of the remainder is called the 
jejunum and the lower three-fifths is known as the ileum. The ileum 
joins that part of the large intestine known as the coecum and at their 
place of union is a marked constriction, called the ileo-coecal valve. 
Fig. 17. The muscular coat is made up of a layer of circular and a 
layer of longitudinal fibers. The mucous membrane is thrown into 
many transverse, or circular, folds which greatly increase its surface, 
and is covered with great numbers of minute elevations, known as the 
villi. It is richly supplied with blood vessels and contains many 
small glands that secrete a liquid, called the intestinal juice. Most 
of the liquid, however, used in the small intestine, is poured into it 
by two large glands, the liver and the pancreas, that connect with it 
by ducts. 

The Liver is situated immediately below the diaphragm on the 
right side and is the largest gland in the body. It weighs about four 



DIGESTION. 65 

pounds and is separated into two main divisions, or lobes. It has a 
complex structure and differs from the other glands in several par- 
ticulars. It receives blood from two distinct sources — the portal vein 
and the hepatic artery. The portal vein carries the blood in its return 
flow from the stomach, intestines, and spleen. It is loaded with food 
materials, but contains little or no oxygen. The hepatic artery, 
branching from the aorta, carries blood containing oxygen. In the 
liver the portal vein and the hepatic artery divide and subdivide until 
they empty into a single system of capillaries surrounding the liver 
cells. The capillaries in turn empty into a single system of veins 
which unite to form the large hepatic vein. This empties into the 
inferior vena cava. 

The liver is more or less active at all times and secretes daily two 
or three pounds of a yellowish, alkaline liquid called bile. On its 
under side is a small membranous sac which serves as a reservoir for 
the bile and is called the gall bladder. The bile passes from the gall 
bladder and from the right and left lobes of the liver by three separate 
ducts which unite to form a common tube which, blending with the 
duct from the pancreas, empties into the duodenum. Though usually 
described as an organ of digestion, the liver has other functions of 
equal or greater importance. (Pages 73 and 88.) 

The Pancreas is a tapering and somewhat wedge-shaped gland 
and is so situated that its larger extremity or head, is encircled by the 
duodenum. From here the more slender portion extends across the 
abdominal cavity nearly parallel to and behind the lower part of the 
stomach. It has a length of six or eight inches and weighs from two 
to three and one-half ounces. Its secretion, the pancreatic juice, is 
emptied into the duodenum by a duct which, as a rule, blends with the 
duct from the liver. 

Intestinal Digestion. The bile partakes more of the nature of 
a waste product than of a digestive fluid. However, it possesses 
properties that enable it to be utilized in the food canal in a variety of 
ways : 

1. Since it is alkaline, it counteracts the acid of the stomach, 
producing an alkaline condition which is necessary for the action of 
the pancreatic juice. 

2. It increases the peristaltic action of the intestines by acting 
as a stimulus to the muscular coat. 



66 ELEMENTS OF PHYSIOLOGY. 

3. It is an antiseptic substance and retards the decomposition of 
food in the intestines. 

4. It furnishes a large bulk of liquid which helps to move the 
contents of the intestines along. 

5. It probably assists in the digestion of the fats. 

The principal constituents of pancreatic juice are water, salts, 
and three different enzymes, or ferments — trypsin, amylopsin, and 
steapsin. These constituents make pancreatic juice the most impor- 
tant of the digestive fluids. It acts vigorously on all classes of foods. 

1. It changes starch into sugar, completing the work begun by 
the saliva. This action is due to the amylopsin which is similar to 
ptyalin, but is more vigorous. 

2. It changes proteids into proteoses and peptones, completing 
the work of the gastric juice. This is accomplished by the trypsin 
which is similar to, but more active than the pepsin. 

3. It is the chief agent in the digestion of fat. In this work 
the active agent is the steapsin. 

Experiments, 1. Prepare artificial pancreatic juice by chopping fine the pan- 
creas of a recently killed pig and soaking it in a one per cent solution of sodium 
carbonate in water. After some hours, strain off the liquid which is then ready 
for use. Add some of this liquid to a thin solution of starch paste, prepared as 
in a previous experiment, and keep in a warm place for five or ten minutes. Xote 
change in appearance and test for presence of sugar with potassium hydroxide 
and copper sulphate. (Page 61.) 

2. Mince a piece of the white of a boiled egg and add to it a considerable 
amount of the solution from the pancreas. Keep for a few hours in a warm place 
and examine. 

Extract of the pancreas, obtained from the drug store, may be substituted 
in this experiment for the fresh specimen. 

The intestinal juice assists in bringing about an alkaline condi- 
tion in the small intestine and probably aids in reducing cane sugar to 
glucose. It is secreted only in small quantities. 

Digestion of Fat. Several different theories have been pro- 
posed regarding the digestion and absorption of fat. Among these, 
what is known as the "solution theory" seems to have the greatest 
amount of evidence in its favor. According to this theory, the fat, 
under the influence of the steapsin, absorbs water and splits into fatty 
acid and glycerine. This finishes the process so far as the glycerine 
is concerned as it is soluble in water, but the fatty acid which is insol- 
uble in water requires further treatment. It is supposed to be acted 



DIGESTION. 67 

upon in one, or both, of the following ways : 1. To be dissolved as 
fatty acid by the action of the bile (since bile is capable of dissolving 
it under certain conditions). 2. To be combined with sodium car- 
bonate and converted into soluble soap. 

The emulsion of fat, by which it is separated into minute particles 
but not changed chemically, is known to occur in the intestine. Tbis 
process, according to the solution theory, is not one of digestion, but a 
process which accompanies and aids in the conversion of fat into 
glycerine and fatty acid. 

Work of the Small Intestine. The small intestine is prob- 
ably the most important division of the alimentary canal. It serves 
as a contrivance for holding the food while it is being acted upon ; 
it secretes the intestinal juice, mixes the food with the digestive 
fluids, propels it toward the large intestine, and, in addition, serves as 
an organ of absorption. 

Digestion is practically accomplished in the small intestine and 
the greater portion of the reduced food is here absorbed. There is 
always present, however, a variable amount of material that is not- 
digested. This, together with a considerable volume of liquid, is 
passed into the large intestine. 

Work of the Large Intestine. The large intestine serves 
as a receptacle of materials from the small intestine. The digestive 
fluids continue their action on the food and the digested materials also 
continue to be absorbed. In these respects the work of the large intes- 
tine is similar to that of the small. It does, however, a work peculiar 
to itself in that it collects and retains undigested food particles, to- 
gether with other waste, and ejects them periodically from the canal. 

The large intestine is from five to six feet in length and aver- 
ages about one and one-half inches in diameter. Its divisions are 
shown in figure 17. 

Work of the Alimentary Muscles. The mechanical part of 
digestion is performed by the muscles which encircle the canal. Their 
chief uses, which have been mentioned in connection with the different 
organs, may here be summarized: 1. They supply the force neces- 
sary for the mastication of the food. 2. They propel the food through 
the canal. 3. They mix the food with the different juices. 4. At 
certain places like the pyloric end of the stomach they partly, or com- 
pletely, close the passage until a process of digestion is completed. 



,;v ELEMENTS OF PHYSIOLOGY. 

Health Suggestions. The following simple rules are familiar 
to nearly everybody and their purpose generally understood : 1. Eat 
slowly and masticate the food thoroughly. 2. Avoid eating between 
meals. 3. Drink sparingly of liquids during meals. 4. Xever 
swallow large particles of food, that are not well masticated. 5. 
Obey your natural appetite and do not think too much about what you 
eat or drink. 

Dangers from Impure Food. Food is frequently the carrier 
of disease germs and for this reason requires close inspection. Typhoid 
fever generally finds its way into the body through impure water. 
Heat is destructive to disease germs, or bacteria, and one safeguard 
against questionable food is thorough cooking. Too much care cannot 
be exercised with reference to water for drinking purposes. Water 
which is not perfectly clear, which has an odor, or which forms a sedi- 
ment on standing, is not fit to drink. It can be rendered compara- 
tively harmless, however, by boiling for some time. When this is 
done it should be boiled the day before it is used in order to give it a 
chance to cool, settle, and take up new air. 

Care of the Bowels. Frequently, through lack of exercise or 
through negligence in evacuating the bowels, a weakened condition of 
the muscles of the food canal is induced that results in the retention 
of waste beyond the time when it should be discharged. This is a 
great annoyance and, at the same time, a menace to health. In addi- 
tion to the irritating effects of the retained material, waste products 
are reabsorbed into the system and circulated over the body by the 
blood. In most cases this condition can be relieved and prevented 
from recurring by observing the following habits : 1. Have a regular 
time each day for evacuating the bowels. 2. Drink a cup of cold 
water on rising in the morning. 3. Eat generously of fruits and 
coarse foods such as oatmeal, corn bread, etc. 4. Persistently prac- 
tice such exercises as bring the abdominal muscles into play. 

Do not rely upon patent medicines, pills, etc., as they usually 
leave the canal in a weakened condition. When in need of help con- 
sult a physician. 

Effect of Beverages. Alcoholic beverages when taken in any 
but very small quantities, have an injurious effect upon the stomach 
and the liver. Tea and coffee, while they may exert beneficial effects 
in small quantities, are liable to interfere with the digestive processes it 
taken in large quantities. 



DIGESTION. 69 

Summary. By digestion, food substances are reduced to such 
a condition that they may he introduced into the circulation. While 
a few substances need simply to be dissolved, most foods must be con- 
verted into substances that are soluble and dialyzable. Digestion, 
therefore, is, to a large extent, a chemical process. The digestive 
fluids supply water, which acts as a solvent and carries important active 
agents, called enzymes, that accelerate the changes. The alimentary 
muscles perform the mechanical work of digestion, while the nervous 
system controls and co-ordinates the various organs. 

Review Questions. 1. State the purpose of digestion. How does di- 
gested food differ from that not digested? 

2. Name the different classes of food that must be reduced to soluble sub- 
stances in the process of digestion. 

3. Name the divisions of the canal in the order that the food passes through 
them. 

4. What is gained by mastication? Why should this process precede the 
others ? 

5. What is the work of the tongue in digestion? 

6. Why should a weakness of the muscular coat interfere with the digestive 
processes ? 

7. Describe the work of the stomach. 

8. Give reasons for regarding the small intestine the most important di- 
vision of the food canal. 

9. At what place and by the action of what liquids are fats, proteids, starch, 
and cane sugar digested? 



CHAPTER X. 



ABSORPTION, STORAGE, AND ASSIMILATION. 



Digested food to reach the cells must first be transferred to the 
blood stream. The process is known as absorption. In general, ab- 
sorption means the penetration of a liquid into the pores of a solid, and 
takes place according to the simple laws of molecular movements. 
Physiological absorption is, however, not a simple process, since other 
than molecular forces are involved and the passage takes place through 
an active (living) membrane. Another difference is that certain foods 
undergo chemical change while being absorbed. 

The Small Intestine as an Organ of Absorption. While 
absorption may occur to a greater or less extent along the entire length 
of the alimentary canal, most of it takes place in the small intestine. 
Its great length, its small diameter, and its blood vessels all adapt the 
small intestine to the work of absorption. The transverse folds in the 
mucous membrane, by retarding the food in its passage and by increas- 
ing the surface, also aid in the process. Of greater importance, how- 
ever, are the minute elevations that cover the surface of the mucous 
membrane, known as 

The Villi. Each single elevation, or villus, is about one- 
fiftieth of an inch long, has a diameter about half as great, and con- 
tains the following essential parts : 1. 
An outer layer of epithelial cells, rest- 
ing upon a connective tissue support. 
2. A small lymph tube which occupies 
the center and connects at the base with 
other lymph tubes, called lacteals. 3. 
A network of capillaries. Fig. 18. 

The villi are the only structures 
that are especially adapted to the work 
of absorption and they are found only 
in the small intestine. The mucous 
membrane, however, in all parts of the 
canal, is capable of taking up more or less of the digested materials. 

70 




18 
Small artery. 2. A lacteal 



s- 



minal lymph tube 
Epithelial cells, t 



3. Ter- 

4. Capillaries. 5. 
Small vein. 



ABSORPTION, STORAGE, AND ASSIMILATION. 71 

The Capillaries and Lacteals act as receivers of material as 
it passes through the layer of epithelial cells covering the mucous 
membrane. The lacteals take up only the digested fat, while the capil- 
laries receive all the other kinds of food. From their terminals in 
the villi, the lacteals extend through the mesentery and connect with 
the thoracic duct. They are called lacteals because of their milk-like 
appearance, given them by the absorbed fat. 

The capillaries in the mucous membrane of the small intestine 
and other parts of the canal, empty into small veins that unite with the 
branches of the portal vein, through which the blood is passed to the 
liver. 

Passage of Different Materials through the Epithelial 
Layer. The layer of epithelial cells, lining the mucous membrane, sep- 
arates the contents of the alimentary canal from the fluids of the body 
'proper. It serves both as a membrane through which osmosis may 
take place and as an active agent in bringing about chemical changes 
in the substances as they pass through. These changes are necessary 
in the economy of the body and vary with the different foods, as fol- 
lows : 

The Carbohydrates which, during digestion, were changed into 
maltose and the different forms of glucose, are, by absorption, changed 
into the form of glucose known as dextrose. 

The proteids which were changed into proteoses and peptones are 
converted into the proteids of the blood, the chief of which is serum 
albumin.* 

The fat which was changed into glycerine, fatty acid and soluble 
soap, is formed again into fat by the union of the glycerine with the 
fatty acid and the soluble soap. 

Water which has undergone no change in digestion, undergoes 
no change in absorption. Its passage takes place, as far as can be dis- 
covered, according to the laws of osmosis and the greater portion of it 
is absorbed from the small intestine. 

The salts are thought to be absorbed according to osmotic 
laws and to undergo no change in their passage through the epithelial 
layer. It is possible, however, that the protoplasm of the epithelial 
cells influences their passage. 

* The necessity for this change is proven by the fact that proteoses and pep- 
tones when injected into the blood as such act as poisons. 



72 



ELEMENTS OF PHYSIOLOGY 



Routes to the Circulation. The absorbed material does not 
rind its way at once into the general circulation, but is conducted by 
special channels, or routes, to places where it can be admitted most 
advantageously. There are two such routes — one is that taken by the 
fat: the other is the one taken by all the remaining food substances. 
Fig. 19. 

1. Route taken by the fat. The fat entering the villi from the 
intestinal canal, finds its way into the lacteals and by them is conveyed 

to the receptacle of the chyle. At this 
place the fat mingles with the lymph 
from the lower part of the body and 
with it passes through the thoracic 
duct to the left subclavian vein. Thus, 
to reach the general circulation, the 
fat must pass through the villi, lac- 
teals. receptacle of the chyle, and the 
thoracic duct. Its passage through 
these places, like the movements in all 
lymph vessels, is quite slow and it is 
only gradually admitted to the blc 
stream. 

2. Route of all substances ex- 
cept fat. Water, salts, carbohydrates. 
and proteids, in passing through the 
layer of epithelial cells, enter the capil- 
laries. Here they mix at once with 
the blood and in a sense are already in 
the general circulation. But this blood 
instead of flowing directly to the heart 
is passed through the portal vein to 
the liver. Here it enters a second set 
of capillaries and. by them, is brought 
very near the liver cells. After undergoing important changes in the 
liver it passes through the hepatic vein into the inferior vena cava. 
This route then, includes the capillaries in the mucous membrane, 
branches of the portal vein, the portal vein proper, the liver, and the 
hepatic vein. In passing through the liver a large portion of the food 
material is temporarily retained for a purpose and in a manner now to 
be explained. 




big 

1. Receptacle of chyle. 2. Lacteals. >:. 
Portal vein. 4. Inferior vena cava. 5. 
Hepatic vein. 6. Position of -ear:. 7. 
Left subclavian vein. S. Left jugular 



ABSORPTION, STORAGE, AND ASSIMILATION. 73 

Storage of Nutriment. The rapid absorption which takes 
place at the alimentary canal, at intervals corresponding to the taking 
of food, introduces into the body proper, food materials faster than the 
cells can make use of them. Following these intervals are periods 
when the body is taking no food but during which the cells must be 
supplied with nutriment. It also happens that the total food absorbed 
during a prolonged interval may be in excess of the needs of the cells 
during that time, while it is always possible, as in disease, to encoun- 
ter conditions when the material absorbed does not equal that con- 
sumed. To keep up a uniform supply of material for the cells and 
to provide for emergencies, it is necessary that the body accumulate 
food materials in excess of its immediate needs. 

The Method of Storage differs with the various food sub- 
stances as follows: 

1. The carbohydrates are found chiefly in three places in the 
body, — the blood, the muscles, and the liver. That in the blood is 
mostly in the form of dissolved dextrose and is ready for use. That 
in the muscles and liver is in the form of glycogen — the form in 
which carbohydrates are stored. It is one of the functions of the liver 
to collect the dextrose from the blood, to change it to glycogen, and to 
retain it until needed by the cells. There is always present in the 
blood a small amount of dextrose, and as this quantity is drawn upon 
by the cells, the glycogen in the liver changes back to dextrose, dis- 
solves, and flows out into the blood. The glycogen in the muscles is 
in small quantities and is consumed by the muscle cells as occa- 
sion demands. Another method of storing the carbohydrates is that 
of converting them into fats. 

2. The fat which is awaiting oxidation in the body may be 
found either in the blood plasma or distributed among the various 
tissues. Certain of the connective cells possess the property of tak- 
ing up the fat from the blood and of depositing it in their protoplasm. 
When this is done to excess and the cells become filled with fat they 
form adipose tissue. This tissue is found chiefly under the skin and 
in places where it fills out inequalities. The fat in the blood is in 
small quantities, except for a time after each period of digestion, 
when the quantity is somewhat increased. 

3. The proteids form a part of all the tissues of the body and 
for this reason are accumulated in larger quantities than any of the 
other food substances. They are also found in relatively large quan- 



74 ELEMEXTS OF PHYSIOLOGY. 

tities in the blood, where they are designated "circulating proteids." 
When eaten in excess, proteids may also be converted, in part, to 
glycogen at the liver. The proteids in the various tissues serve the 
double purpose of forming a working constituent of the cell proto- 
plasm and of supplying reserve food material. That the tissue pro- 
teid is used to liberate energy in the body and, in this way, serves as 
storage material is shown by the rapid loss of proteids in starving 
animals. 

Other facts of interest relating to the storage of food are : 

1. The form into which a food is converted for storage is of 
the nature of a solid which can be changed back to its former condi- 
tion and re-enter the blood. 

2. Only energy-yielding foods are stored. Water and salts, 
while they may be absorbed in excess of the needs of the body are not 
stored by conversion into other substances. 

3. The interval of storage may be long or short corresponding 
to the needs of the body. 

4. In the consumption of storage material the glycogen is used 
first, then, as a rule, the fat, and last of all the proteid. 

Regulation of Food Supply to the Cells. The storage of 
foods not only enables the body to supply the needs of the cells during 
intervals when no food is taken, but also provides a means for regulat- 
ing the rate of the supply of materials to the cells. The cells obtain 
their materials from the lymph and the lymph is supplied from the 
blood. When food substances, such as sugar, increase in the blood 
beyond a low per cent, they are converted into a form, like glycogen, 
in which they are held in reserve, or, for the time being, placed be- 
yond the reach of the cells. When, however, the supply in the blood 
is being reduced, the stored material re-enters the blood and again 
becomes available to the cells. In this way the rate of supply may 
be practically constant. 

We are now in a position to understand why carbohydrates, fats, 
and proteids are so well adapted to the needs of the body, while other 
substances like alcohol, which liberate energy, prove injurious. 

Why Alcohol is not a Food. If the passage of alcohol 
through the body be followed it is seen, in the first place, that it under- 
goes no digestive change, and in the second place, that it is rapidly 
absorbed from the stomach in both weak and concentrated solutions. 
This introduces it quickly into the blood and, once there, it diffuses 



ABSORPTION, STORAGE, AND ASSIMILATION. 75 

rapidly into the lymph and then into the cells. Since it cannot be 
stored as alcohol or converted into some storage substance like fat,* 
or glycogen, there is no way of regulating the amount that shall be 
present in the blood, or of supplying it to the cells as their needs re- 
quire. They must take it in whatever quantities it is introduced 
into the body, regardless of the effect. It is thus seen that, since 
alcohol is not adapted to the body's plan of taking up material and 
supplying it to the cells, it cannot be classed as a food. 

Assimilation is the appropriation of food material by the 
cells. In a sense the storage of fat by connective tissue cells and of 
glycogen by the liver cells is assimilation. The term, however, is 
limited to the taking up of material that is to be used by the cell in 
serving its own purposes. Whether all of the materials used by the 
cells actually become a part of their protoplasm, is not known. It 
is known, however, that in the protoplasm of the cells is where 
the oxidations of the body occur and that materials taking part in 
these oxidations must, at least, come in close contact with the pro- 
toplasm. Assimilation is then the last event in a series of processes 
by which oxygen, food materials, and the cell protoplasm are brought 
into close and active relations with each other. Table I. 

Enzymes. The chemical changes in digestion, absorption, 
storage, and assimilation, as well as the oxidations at the cells, are 
brought about, to a large extent, by the action of a class of substances, 
called ferments, or enzymes. These are found in the digestive fluids, 
as already noted, and also in the different tissues. They are like- 
wise the cause of certain chemical changes that occur outside of the 
body, such as fermentation and decay. Some of the characteristics 
of enzymes are as follows: 

1. They require a certain temperature for their action. 

2. They are destroyed if the temperature is too high. 

3. They are not used up in the process like the ordinary chem- 
ical reagents. 

4. Their action is checked by an excess of the material which 
they form and, under certain conditions, is reversed. 

From a chemical standpoint enzymes are classed with substances 

* The fat that results from the excessive use of beer is due to the diminished 
oxidation of fats and carbohydrates and is in no sense a conversion of alcohol 
into fat. 



76 



ELEMENTS OF PHYSIOLOGY. 



that act by their presence to influence chemical reactions and are 
known as catalytic agents. 



TABLE I. THE PASSAGE OF MATERIALS TO THE CELLS. 



Materials. 


Digestion. 


Absorption. 


Route to the 

general 

circulation. 


Storage. 


Condition in 
the blood. 


Proteids. 


Changed into 
proteoses and 
peptones by 
the action of 
the gastric 
and pancre- 
atic juices. 


In passing 
into the cap- 
illaries, the 
proteoses and 
pepton es 
change into 
the albumins 
of the blood. 


Through the 
portal vein to 
the liver and 
from there 
through the 
hepatic vein 
into the infe- 
rior vena cava. 


Become a 
part of the 

protoplasm of 
all the'cells. 


As albumins 
in colloidal 
solution. 


Fat. 


Changed into 
fatty acid, 
glycerine and 
soluble soap 
by the bile 
and pancre- 
atic juices. 


In passing 
into the lac- 
teals, the gly- 
cerine unites 
with the solu- 
ble soap and 
fatty acid to 
form the oil 
droplets of 
the blood. 


Through the 
lacteals to the 
thoracic duct 
by which it is 
emptied into 
the left sub- 
clavian vein. 


As fat in the 
cells of con- 
nective tissue. 


Chiefly as 
minute drops 
of oil. 


Starch. 


Reduced to 
some of the 
different 
forms of 
sugar as malt- 
ose or glu- 
cose. 


Enters the 
capillaries as 
a form of glu- 
cose, called 
dextrose. 


Through por- 
tal vein, liver, 
hepatic vein 
into the infe- 
rior vena cava. 


As glycogen 
chiefly by the 
liver but to 
some extent 
by muscle 
cells. 


As a form of 
glucose in 
solution. 


Water. 


Undergoes no 
change. 


Taken up 
both by the 
lacteals and 
capillaries but 
to the greater 
extent by the 
capillaries. 


Takes both 
routes, but 
passes in 
larger quanti- 
ties via the 
liver. 


Is not stored 
in the sense 
that energy 
foods are. 


As the water 
which serves 
as a carrier of 
all the other 
constituents 
of the blood. 


Salts. 


Undergo no 
change. 


Taken up by 
the capilla- 
ries without 
undergoing 
a pparent 
change. 


Pass via the 
portal vein, 
liver, and 
hepatic vein 
into the in- 
ferior vena 
cava. 


Not stored in 
the body. 


In solution. 


Oxygen. 




Taken up by 
the capillaries 
at the lungs. 






United with 
the haemoglo- 
bin and to a 
small extent 
in solution in 
the plasma. 



ABSORPTION, STORAGE, AND ASSIMILATION. 77 

Summary. Digested food material is taken up by the capil- 
laries and the lymph vessels and transferred by two routes to the cir- 
culation. In passing through the epithelial lining of the canal the 
more important foods undergo changes that adapt -them to conditions 
found in the blood stream. Since materials are not to be used as 
rapidly as they are taken up, provisions are made for storing them 
in the body and for supplying them to the cells as their needs require. 
In the production of the chemical changes incident to digestion, ab- 
sorption, and storage of food, as well as the oxidation at the cells, 
the presence of active agents called enzymes is necessary. 

Review Questions. 1. How does the absorption of food material differ 
from that of a liquid by a solid ? 

2. In what respects is the small intestine especially adapted to absorption? 

3. What are the parts of a villus? What are the lacteals? 

4. What part is played by the capillaries and lacteals in the work of ab- 
sorption ? 

5. What changes, if any, take place in water, salts, fats, and carbohydrates 
during absorption? 

6. What double purpose is served by the epithelial layer ? 

7. Trace the passage of proteids, fats, and carbohydrates from the small 
intestine to the general circulation. 

8. What is the necessity for storing up foods in the body? Why is it not 
also necessary to store up oxygen? 

9. In what form is each of the principal classes of foods stored? 

10. How is the rate of supply of food to the cells regulated? Why is the 
body unable to regulate the supply of alcohol to the cells when this substance is 
taken ? 

11. How does assimilation differ from storage of food materials? 

12. What role is played by the enzymes in the body? What enzymes are 
found in each of the digestive fluids? 



CHAPTER XI. 

LIBERATION OF ENERGY IN THE BODY. 

Energy. The human body, in common with all the higher an- 
imal forms, is characterized by movements, bodily warmth, and com- 
plex internal processes. All these activities are brought about 
through the expenditure of energy. Energy is power. It may be 
stored up in a body, or it may be in the condition of being expended. 
In the former state it is known as potential, or latent energy ; in the 
latter as kinetic, or active, energy. The reserve energy of the body 
is potential. It becomes kinetic as it is being used in various ways. 

Nature of Potential Energy. Much of the potential en- 
ergy about us is due to the manifest tendency of substances to col- 
lect into larger masses and to form various combinations. While 
this tendency is not understood, it may be conveniently thought of as 
a kind of attraction, and different forms of it, as gravitation, cohe- 
sion, etc., are recognized. If two bodies having an attraction for each 
other are separated they tend to move toward each other. Since they 
have the capability of motion they possess energy. The storing of 
energy in such bodies is simply a matter of separating them. Thus 
if a stone is raised above the earth gravitation may cause it to return, 
or if rubber is stretched cohesion may cause it to shorten again. In 
all such cases the energy expended in producing the separation be- 
comes potential and so remains as long as the separation exists. 

Chemical Potential Energy. While there are different 
forms of potential energy as suggested above, that known as chemical 
potential energy is of chief importance in its relation to the body. 
This form is made possible by the existence of a force called chem- 
ical affinity or chemism. Chemism is the attraction between atoms, 
the smallest particles found in matter. A body possesses chemical 
potential energy when its atoms are separated from the atoms of 
other bodies for which they have attraction. Gunpowder is a good 
example of a substance having chemical potential energy. It is pre- 

78 



LIBERATION OF ENERGY IN THE BODY. 79 

pared by mixing (not uniting) in correct proportions, sulphur, car- 
bon, and a compound called potassium nitrate, which is rich in oxy- 
gen. The atoms of the sulphur and carbon have a strong attraction 
for the atoms of oxygen. When the temperature of the powder is 
raised sufficiently the atoms move toward each other and unite to 
form new compounds. In this way their potential energy, becomes 
kinetic, causing the explosion. 

Nature's Storehouse of Energy. In a somewhat similar 
manner, the earth's greatest supply of potential energy is made pos- 
sible. In the atmosphere is found a large amount of free oxygen. 
On the earth are many substances which contain elements, the atoms 
of which have a strong affinity for the atoms of oxygen. By com- 
plying with certain known conditions a union between these elements 
and oxygen is brought about. Combustion is the result of such a 
union. It thus happens that the oxygen of the air on the one hand 
and the products of plant life — wood, coal, etc. — on the other hand, 
because of the mutual attraction of their atoms, and their condition of 
separation, provide a great supply of chemical potential energy. 

For the keeping up of this supply we are dependent upon veg- 
etation. In the separation of carbon dioxide into carbon and oxygen 
(p. 43), the plant places these elements in such a condition that they 
are again able to unite. The sunlight, which works through the 
plant, is the real cause of the separation and the energy of the sepa- 
rated oxygen and carbon is in a sense the stored up energy of the sun. 

Forms of Kinetic Energy. In the burning of wood the chemical potential 
energy of the oxygen of the air and the carbon of the wood is transformed into 
kinetic energy. This appears in the form of beat and also of light. If the heat 
is applied to water, steam is produced, which may cause the motion of machinery, 
and this by turning a dynamo causes electrical energy. These activities suggest 
the more important forms of kinetic energy, which are heat, light, mechanical 
motion, and electrical energy. These are related, in the sense that all are forms 
of motion, and each is convertible into the other. 

The Energy of the Body. To supply the energy needed 
by the body is one of the most difficult problems of animal life. The 
animal cannot create energy; neither can it, like the plant, use the 
kinetic energy which may come to it from the sun. Its only resource 
is to obtain it in the potential form. To do this it must draw from 
the storehouse of nature and utilize the energy there contained in 
the oxygen of the air and the products of vegetation. This is ac- 



80 ELEMENTS OF PHYSIOLOGY. 

complished by passing the oxygen and food to the cells where the 
conditions are favorable for their union. Until their union occurs 
the energy remains potential, but in the act of uniting it becomes 
kinetic and may be used in the work of the body. 

A fact of importance in the liberation of energy is that the rate 
is just sufficient to supply the needs of the body. It is easily seen 
that too rapid or too slow a rate would prove injurious. The oxida- 
tions at the cells are therefore under control and the quantity of 
energy supplied to the body as a whole and to the different organs 
is proportional to the work that is done. 

Animal Heat and Motion. Most of the body's energy is 
expended as heat and motion. Of the whole amount it is estimated 
that as much as five-sixths is used as heat. The proportion, however, 
varies with different persons and is not constant in the same individual, 
during different seasons of the year. The heat is used in keeping the 
body at that temperature which is best suited to carrying on the vital 
processes. This is 98.5° E. and is called the normal temperature. 
To maintain this temperature uniformly through all the varying con- 
ditions within, and on the outside of the body, requires a very delicate 
adjustment of the heat-producing and regulating processes. All 
parts of the body, through oxidation, furnish heat. Active organs, 
however, such as muscles, the brain, and glands furnish a larger 
share. The blood in its passage through the body serves as a heat 
distributer and keeps the temperature about the same in all parts. 
The production of motion is considered in the study of the muscular 
system. 

Hygiene. The heat producing capacity of the body sustains a 
very important relation to the general health. A sudden chill may 
result in a number of derangements and is the usual cause of colds. 
One's capacity for producing heat may be so low that he is unable to 
respond to a sudden demand for heat, as in going from a warm into a 
cold room. As a consequence, the body is unable to protect itself 
against unavoidable exposures. 

Impairment of the heat-producing capacity is brought about 
in many ways. Several diseases do this directly, or indirectly, 
to quite an extent. In health excessive care in protecting the body 
from cold is perhaps the most potent cause of its impairment. Stay- 
ing in rooms heated above a temperature of 70° F., wearing clothing 
unnecessarily heavy, and sleeping under an excess of bed clothes, 



LIBERATION OF ENERGY IN THE BODY. 81 

diminish the power to produce heat, by accustoming the body to pro- 
ducing only a small amount. Lack of physical exercise in the open 
air, as well as too much time spent in poorly lighted and ventilated 
rooms, tend also to diminish it. Since most of the heat of the body 
comes by the union of oxygen with the food materials in the cells, 
a lack of either will interfere with the production of heat. 

Exhaustion. The energy at the disposal of the body is spent 
in two general ways : First, in carrying on the vital processes and 
second, in the performance of voluntary activities. Since, in all 
cases, there is a limit to one's energy, it is easily possible to expend 
so much in the pursuit of one's business, or in pleasurable exercise, 
that the amount left is not sufficient for the proper maintenance of 
the vital processes. This is the condition when one has overworked 
or has exercised beyond his strength. A lack of energy for the vital 
processes leads to disturbances that render the body less able to obtain 
a requisite supply and in time leads to serious results. The remedy 
in such cases lies in the removal of the cause, and not in the use of 
stimulants. 

Simple Experiments. 1. The change of kinetic into potential energy may 
be shown by stretching a piece of rubber, lifting a body, separating the armature 
from a magnet, and by decomposing water with an electrical current. 

2. The change of potential energy into kinetic may be shown by letting 
bodies fall, releasing the end of a stretched piece of rubber, and by the burning of 
wood. 

3. The change of one form of kinetic energy into another form may be illus- 
trated by rubbing together two pieces of wood until they become heated, by ringing 
a bell, and by causing motion in air and water by heating them. If suitable appa- 
ratus is at hand, the transformation of electrical energy into heat, light, sound, 
or mechanical motion can easily be shown. 

Summary. The body requires a continuous supply of energy. 
To obtain this, materials possessing chemical potential energy are 
introduced. Oxygen and food substances, because of their ability to 
unite chemically in the body, can be utilized for this purpose. So 
long as the foods are not oxidized the energy remains in the potential 
form in the body. In , the process of oxidation the potential is 
changed into kinetic energy and is expended in the form of heat and 
motion, and in other ways. 



6 



82 ELEMENTS OF PHYSIOLOGY. 

Review Questions. 1. What are the proofs that the body possesses en- 
ergy ? 

2. Show that a stone lying against the earth has no energy, while the same 
stone above the earth has energy. 

3. Water is composed of hydrogen and oxygen, which have an attraction for 
each other. Why then does not water contain potential energy? 

4. What kind of energy is possessed by a bent bow, a revolving wheel, a 
coiled spring, the wind? 

5. Why is it necessary to separate bodies having an attraction for each 
other, in order to give them energy? 

6. Account for the energy possessed by the oxygen of the air and food sub- 
stances. 

7. How does the body obtain its supply of energy? 

8. In what different ways dees the body expend its energy ! 

9. How mar over-work or over-exercise injure the bodv? 



CHAPTEE XII. 

THE EXCRETORY WORK OF GLANDS. 

Glands are organs that prepare special liquids in the body and 
pour them out upon free surfaces. These liquids, called secretions, 
are separable into two classes, known as the useful and the useless secre- 
tions. To the first class belong all secretions that are made to serve 
some purpose in the body, while the second includes the liquids sep- 
arated as waste products from the blood. The first are usually desig- 
nated as true secretions, or secretions proper, and the second as 
excretions. The most important glands producing liquids belonging 
to the first class are those of digestion. (Chapter IX.) 

General Structure of Glands. While the various glands 
differ widely in size, form, and purpose, they present striking sim- 
ilarities in structure. The active agents in all the glands are the 
so-called gland, or secreting, cells. These are usually cubical in form 
and are always spread over a connective tissue support, known as the 
basement membrane. Beneath the gland cells and penetrating the 
basement membrane are numerous capillaries and lymph vessels, as 
well as nerve fibers. These structures — gland cells, basement mem- 
brane, capillaries, lymph vessels, and nerve fibers — form the essen- 
tial parts of all glands. The capillaries and lymph vessels supply 
the gland cells with blood, the nerves control the time and rate of 
secretion, while the basement membrane forms a suitable support for 
all these parts. 

Kinds of Glands. Glands differ from each other chiefly in 
the arrangement of their essential parts. The simplest disposition of 
these parts is that of spreading them over a smooth surface as in the 
pleura and the pericardium. Such an arrangement is not usually 
known as a gland, but is called a secreting surface. It produces but 
a small amount of liquid for the surface employed and is not adapted 
to conditions requiring large amounts of liquid. A somewhat more 
complex arrangement is that where the gland elements are made to 

83 



S4 



ELEMENTS OE PHYSIOLOGY. 



the folding, 



in 



line the interiors of small cavities which are formed by 
or pitting, of exposed surfaces. Such glands are found chiefly 
the mucous membrane, especially that lining the alimentary canal. 
In the stomach they are quite numerous, supplying the gastric juice. 
If these glands have the general form of tubes they are called tubular 
glands: if sac-like in shape they are called saeular. or racemose, 
glands. Both the tubular and the saeular glands may, by branching, 
form a great number of similar divisions which are connected with 




if « 



Fig. 20. Evolution of glands. A. Simple secreting surface. 1. Gland cells. 2. Basement 

membrane. 3. Blood vessel. 4. Nerve. B. Simple tubular gland. C. Simple saeular gland. 

D. Compound tubular gland. E. Compound saeular gland. F. A compound racemose gland 

with duct passing to a free surface. G. Relation of food canal to different forms of glands. 



each other and which communicate, by a common duct, with the 
place where the secretion is used. This forms the compound gland 
which, depending upon the structure of the minute parts, may be 
either a compound tubular or a compound racemose gland. The gas- 
tric and the perspiratory glands are good examples of tubular glands, 
while the oil glands of the skin are saeular glands. The large glands, 
such as the pancreas and the salivary, belong to the compound race- 
mose type, while the kidneys are compound tubular glands. Fig. 20. 



THE EXCRETORY WORK OF GLANDS. 85 

Nature of the Secretory Process. The secretions are 
found to contain materials, such as water and salts, that are found in 
the blood. They also contain materials that are not found in the 
blood but have been supplied by the glands. Important changes 
within the gland cells are also known to take place during the time 
of secretion. If, for example, the cells of the pancreas be examined 
microscopically after a period of rest, they will be found to contain 
many small granular bodies. On the other hand, if they be examined 
after a period of activity, the granules have disappeared and the cells 
themselves have become smaller in size. These granules have, no 
doubt, been used in forming the secretion. These facts have led to 
the conclusion that secretion is, in part, a separation of materials from 
the blood and, in part, a process by which specific substances are man- 
ufactured and added to the secretions. 

Excretion, the process of removing waste materials from the 
body, is made necessary by the results attending oxidation at the 
cells. (P. 40.) The final products of oxidation are of such a nature 
that they can no longer take any part in the vital processes. They 
correspond to the ashes and gases that are produced in ordinary com- 
bustion and form so much waste that must be removed. The most 
important of such products are the following: 

1. Carbon dioxide, (C0 2 ) which is formed by the union of 
oxygen with the carbon of the food substances and the protoplasm. 
In its natural condition it is a gas, but in the body it is dissolved in 
different liquids and is in chemical combination. 

2. Water (H 2 0) which is formed in the body, to some ex- 
tent, by the union of oxygen with the hydrogen of food substances 
and to that degree is a waste product, This, however, is but a small 
fraction of the total amount that passes through the body. It is, of 
course, a liquid and as such enters and leaves the body. 

3. Urea* (CO(NH 2 ) 2 ) which is formed by the union of 
oxygen with nitrogenous compounds. It is a solid substance, but 
is soluble in water and while in the body is in solution. 

4. Salts. These comprise a number of different materials 



* In the oxidations that occur in the body it is not supposed that the food 
substances are immediately oxidized to carbon dioxide, water, and urea. On the 
other hand, it is held that the reduction takes place gradually, as in the reduc- 
tion of sugar by fermentation, and that these waste products show only the final 
results. 



ELEMEXTS OE PHYSIOLOGY 



some of which are formed in the body, while others, like common salt, 
enter as a part of the food. They are solids, but leave the body dis- 
solved in water. 

These substances, if left in the body, interfere with its work and 
in a short time cause death. Their removal, which is as necessary 
as the introduction of food materials and oxygen into the body, is 
largely the work of glands. 

General Plan of Excretion. From the cells, where they 
are formed, the waste materials pass into the lymph and from the 
lymph find their way into the blood. As a part of the blood they 
are circulated over the body and at certain places enter the organs, 
by which they are separated. They are then passed to the exterior 
of the body. The glands that serve as excretory organs are the kid- 
neys, liver, and perspiratory glands. 

The Kidneys. The kidneys are two bean-shaped glands sit- 
uated in the back and upper portion of 
the abdominal cavity, one on each side 
of the spinal column. They weigh 
from four to six ounces each, and lie 
between the abdominal wall and the 
peritoneum. Two large arteries from 
the aorta, called the renal arteries, sup- 
ply them with blood, while they are con- 
nected with the inferior vena cava by 
the renal veins. They remove from 
the blood an exceedingly complex 
liquid called the urine, the principal 
constituents of which are water, salts 
of different kinds, and urea. The kid- 
neys pass their secretion by two slender 
tubes, the ureters, to a reservoir called 
the bladder. Fig. 21. 

Minute Structure of the Kid- 
neys. Each kidney is a compound 
tubular gland and is composed chiefly 
of the parts concerned in its work. These consist of many small 
blood vessels and a system of minute tubes called the urintferous 
tubes. Each uriniferous tube starts at the outer margin of the kid- 




Fig. 21. Relations of the kidneys. 
'Back view.; 1. The kidneys. 2. 
Ureiers. 3. Bladder. 4. Aorta. 5. 
Inferior vena cava. 6. Renal arter- 
ies. 7. Renal vein. 



THE EXCRETORY TV ORE OF GLANDS. 



87 




Fig. 22. Enlarged Malpighian capsule and 
uriniferous tube. 1, 2. Blood vessels. 3. 
Epithelial lining of capsule. 1. Lining of the 
uriniferous tube. 



ney in a globular enlargement, called the Malpighian capsule, 

which incloses a cluster of capil- 
laries. Fig. 22. From here the tube 
extends toward the concave side of 
the kidney, where it terminates. Be- 
tween its origin and termination, 
however, are several convolutions 
and one or more loops or turns. 
Finally, after passing a distance 
much greater than from the mar- 
gin to the center of the kidney and 
after joining with other similar tubes, it empties its contents into 
one of the branches of the ureter. The uriniferous tube is lined 
throughout its entire length by secreting cells, which, differing slightly 
at different places, rest upon a basement membrane well supplied 
with capillaries. These cells are the active agents in separating im- 
purities from the blood. 

Blood Supply. The renal artery enters the kidney by four 
branches which, by dividing, send smaller divisions to all parts. At 
the margin of the kidney, called the cortex, the blood is pas.sed through 
two systems of capillaries. The first form 
clusters within the Malpighian capsules 
and receive the blood direct from the small- 
est arteries. The second form a net- 
work around the uriniferous tubes and re- 
ceive the blood which has passed from the 
capillary clusters into a system of small 
veins. From the last system of capil- 
laries the blood is collected into veins that 
pass from the kidneys where the artery 
branches enter and, by uniting, form the 
renal Veins. Fig. 23. In the central 
part of the kidney the blood passes 
through but a single system of capillaries. 

The Work of the Kidneys is 

done in part at the capsules and in part 
along the whole length of the uriniferous 
tubes. Water and salts are removed 
chiefly at the capsules while the remaining 




Fig. 23. Diagram of the circu- 
lation in the kidneys. 1. Small 
branch of renal artery. 2. Small 
branch of renal vein. 3. Arterial 
branches entering capsules. 4. 
Branches of veins. 5. Malpighian 
capsules. 6. Capillaries around 
the uriniferous tubes. 7. Urinif- 
erous tubes. 



88 ELEMENTS OF PHYSIOLOGY. 

solids are removed by the cells that line the tubes. 

The kidneys are the only organs of the body that are purely 
excretory in function. All the others that remove waste have addi- 
tional functions. This fact, together with the service which the kid- 
neys actually render, cause them to be classed as the most important 
of the excretory organs. 

Urea is the most abundant solid constituent of the urine and 
is the chief waste product arising from the oxidation of nitrogenous 
substances. It is not formed, however, by the kidneys nor at the 
muscles where the proteids are broken down in largest quantity. Its 
formation in the body has been found to be the work of the liver and 
to take place as follows: In the tissues the proteids are reduced to 
a lower order of nitrogenous compounds, such as compounds of am- 
monia, which are then taken to the liver where, by the action of the 
liver cells, they are converted into urea. The urea then passes into 
the blood, from which it is separated by the kidneys. 

The Liver as an Excretory Gland. The liver assists in the 
work of excretion in two ways, as follows: 1. By changing waste 
nitrogenous substances into urea, as already stated. 2. By removing 
from the blood the waste products that appear in the bile. 

Along with other waste, the bile contains the products of de- 
composition from the haemoglobin of the red corpuscles. These give 
the bile its characteristic color and are known as bile pigments. The 
bile also contains a substance resembling fat, called cholesterin. which 
is supposed to be a waste product from nervous tissue. Salts of dif- 
ferent kinds also appear in the bile. 

Functions of the Liver. While the chief work of the liver 
is not that of excretion, its functions may here be summarized. The 
liver is, first of all, a manufacturing organ, producing as we have seen 
three distinct products — bile, glycogen, and urea. The nature of 
these substances and their treatment in the body cause the liver to 
be classed as an organ of digestion, a storage organ, and an organ of 
excretion. These functions make of the liver an organ of the first 
importance. 

The Perspiratory or Sweat Glands are located in the skin. 
They belong to the type of simple tubular glands and are very numer- 
ous over the entire surface of the body. 

The sweat glands secrete a colorless, watery fluid called perspir- 



THE EXCRETORY "WORK OF GLANDS. 



89 



ation, or sweat, which contains, besides water, a small per cent of 
salts and nrea. While the excretory work of these glands seems not 
so great as was formerly supposed, they supplement in a practical 
way the work of the kidneys and, during diseases of these organs, 
increase their excretory work to a marked degree. The perspiration 
also plays an important role in the regulation of the temperature of 
the body. (Chapter XV.) 

The Glands of the Food Canal, while secreting liquids that 
are used in digestion, also separate materials from the blood that may 
be regarded as waste. These are passed from the canal along with 
the waste from the liver and the undigested particles of food. 

Excretory Work of the Lungs. While the lungs cannot 
be regarded as glands, they do a work in removing waste from the 
body which must be considered in the general process of excretion. 
As already noted (p. 30) they are especially adapted to removing 
gaseous substances from the blood and it is through them that most 
of the carbon dioxide leaves the body. A considerable quantity of 
water is removed in the form of vapor, as may be shown by breathing 
against a cold window pane. 

TABLE II. THE PASSAGE OF WASTE MATERIALS FROM THE CELLS. 



Materials. 


State to which 
they belong. 


How formed 
in the body. 


Condition in 
the blood. 


How removed from the 
blood. 


Carbon dioxide. 


Gaseous. 


By the oxida- 
tion of the 
carbon of nro- 
teids, carbo- 
hydrates, and 
fats. 


Dissolved in 
the plasma 
and in loose 
combination 
with salts in 
the blood. 


Separated from the blood at 
the alveoli of the lungs and 
then forced through the air 
passages to the outside atmos- 
phere. 


Urea. 


Solid. 


By the oxida- 
tion at the 
tissues and in 
the liver of 
nitrogenous 
compounds. 


Dissolved in 
the plasma. 


Removed by the uriniferous 
tubes of the kidneys and, to 
a small extent, by the per- 
spiratory tubes. 


Water. 


Liquid. 


By the oxida- 
tion of the hy- 
drogen of pro- 
teids, carbo- 
hydrates, and 
fats. Amount 
formed in the 
body Is small. 


As water. 


Removed by all the organs of 
excretion, but in the largest 
quantities by the kidneys and 
skin. 


Salts. 


Solid. 




In solution. 


By the kidneys and skin. 



9< » ELEMENTS OF PHYSIOLOGY. 

Quantity of Excretory Products. If the weight of the 

normal body be taken at interval?, after growth has been attained, 
there will he found to be practically no gain or loss from time to 
time. This shows that materials are leaving the body as fast as they 
enter * and that the tissues are being torn down as rapidly as they 
are built up. It also shows that substances do not remain in the 
body permanently but only so long, perhaps, as is necessary for them 
to give up their energy, or to serve some additional purpose in the 
everchanging protoplasm. The excretory organs then remove from 
the body a quantity of material that is practically equal in weight 
to the material absorbed at the organs of digestion and respiration. 
This is estimated for the average individual to be about five pounds 
daily. 

Ductless Glands. Midway in function between the glands that secrete use- 
ful liquids and those that remove waste materials from the blood, is a class of 
bodies found at various places known as the ductless glands. They are so 
named from their general form, which is similar to that of glands, and not from 
their structure, which is usually different. As their name implies, they possess 
no external openings or ducts. They are in communication, however, with the 
circulation and are supposed to act upon the blood, either by removing substances 
from it or by manufacturing and adding substances to it. The most important 
of the ductless glands are the spleen, the thyroid gland, the suprarenal bodies., 
and the thymus gland. 

Health Suggestions. Physical exercise, by increasing the 
circulation, facilitates the work of excretion, especially that done by 
the skin. The work devolving upon the kidneys may be lessened by 
keeping the skin clean and active. The kidneys may also be saved 
extra and useless work by avoiding an excess of proteid foods, such 
as meats. To a certain point proteids are needed as tissue builders, 
but if taken beyond this they are reduced by the liver to glycogen 
and urea before reaching the tissues. Tor this reason an excess of pro- 
teids may overwork both the liver and the kidneys. A condition of 
inactivity of the bowels should, if possible, be avoided as this leads 
to reabsorption of waste in the food canal. As a rule the work of 
excretion is also facilitated by drinking freely of pure water. This 



* As a matter of fact, a small per cent of the material does find permanent 
lodgment, chiefly in the bones and connective tissue., and to some extent in all the 
tissues. Its presence is indicated by the changes that the tissues undergo with 
age. 



THE EXCRETORY WORK OF GLANDS. 91 

liquid, acting as the natural solvent and transporter of waste ma- 
terial, has these essential qualities increased, by an increase, within 
certain limits, of the amount taken into the body. 

Summary. As a result of the oxidations at the cells, substances 
are produced which can no longer serve a purpose in the bod;y. They 
are of the nature of waste and their continuous removal is as necessary 
to the maintenance of life as the introduction of food and oxygen. 
The organs whose work is to remove the waste, excepting the lungs, 
are glands ; and the materials which they remove are of the nature of 
useless secretions. From the cells, the waste passes through the lymph 
into the blood. From the blood it is separated by the excretory organs 
and passed to the exterior of the body. 

Review Questions. 1. What general purposes are served by the glands in 
the body ? 

2. What are the parts common to all glands ? What purpose is served by 
each of these parts ? 

3. Trace the evolution of glands from the simple secreting surface. How 
do tubular differ from sacular glands ? 

4. Describe the nature of the secretory process. 

5. What conditions render necessary the formation of waste substances in 
the body? Why must they be removed? 

6. How do impurities get from the cells to the organs of excretion? 

7. In what do the uriniferous tubes have their beginning? In what do they 
terminate? With what are they lined? 

8. Bright's disease of the kidneys affects the uriniferous tubes and interferes 
with their work. What impurity is then left in the blood? 

9. Trace water and salts from where they are removed from the blood 
through the different tubes to the bladder. 

10. Trace carbon dioxide from the cells to the outside atmosphere. 



SUMMARY OF PART I. 

Onr study so far has shown that the body is an aggregation of 
different kinds of cells ; that it grows by the growth and reproduction 
of these cells : and that its life as a whole is maintained by keeping 
them alive. For ministering to the wants of the cells two liquids 
(the lymph and the blood) are employed. To keep the blood and 
lymph in the proper condition for ministering to the cells the organs 
of circulation, respiration, digestion, secretion, and excretion are em- 
ployed. Through the combined action of these organs two general 
movements of materials are kept up in the body, as follows: 

1. An inward movement which carries material from the out- 
side of the body toward the cells. 

2. An outward movement which carries material from the cells 
to the outside of the body. 

Passing inward are the oxygen and food materials in a condition 
to unite with each other and thereby change their potential into kinetic 
energy. Passing outward are the oxygen and the elements that formed 
the food material after they have united at the cells and liberated their 
energy. (Fig. 1.) 

As a final and all important result there is kept up a continuous 
series of chemical changes in the cells. These liberate energy, pro- 
vide material for the growth and repair of the tissues, and preserve 
the life of the bodv. 



92 



PART II. 



MOTION, CO-ORDINATION, SENSATION, 



CHAPTER XIII. 

THE SKELETON. 

The Tissues Employed in the construction of the skeleton, 
or framework of the body, are the osseous, cartilaginous, and connect- 
ive and are known as the supporting tissues. They form the bones, 
supply the elastic pads at their ends and furnish strong bands, or lig- 
aments, for fastening them together. The tissues of the skeleton pos- 
sess properties that adapt them to their purposes. The separate units 
or parts from which the skeleton is constructed are the bones. These, 
as usually estimated, are 208 in number and vary greatly in size and 
shape. 

The Properties and Composition of Bone are indicated to 
some extent by the following 

Experiments: 1. Examine a slender bone, like that in the leg of a chicken. 
Note that it resists bending and is difficult to break. Note also that when slightly 
bent it will spring back. 

2. Soak such a bone over night in a mixture of one part of hydrochloric acid 
and four parts of water. Then ascertain by bending, stretching and twisting what 
properties, if any, the bone has lost. 

3. Burn a small piece of bone in a clear gas flame, or on a bed of coals, until 
it ceases to blaze and becomes white in color. Can the bone now be bent or 
twisted? What properties has it lost, and what retained, by the burning? 

The acid dissolves the material which gives the bone its prop- 
erty of stiffness. This is called the mineral matter and consists, 
chiefly of phosphate and carbonate of calcium. 

93 



94 



ELEMENTS OF PHYSIOLOGY. 



Burning, on the other hand, destroys the material which gives 
the bone its toughness and elasticity. This is called the animal mat- 
ter. This consists mainly of a substance, called ossein, which can 
be removed from the bones by boiling and is then known as gelatine. 
The blood vessels and nerves in the bone and the protoplasm of the 
bone cells are also counted in with the animal matter. 

If a bone from a full grown, but not old animal be weighed 
before and after being burned, it will be found to have lost about 
one-third of its weight. From this we may conclude that one-third 
of the bone by weight is animal matter and two-thirds is mineral. 
This proportion, however, varies with age, the mineral matter in- 
creasing with advance of years. 

The Gross Structure of Bone is best learned by studying 
both dry and fresh specimens, as follows: 

Observations. 1. Procure a long, dry bone. One that has lain out in a 
field until it has bleached will answer the purpose excellently. Test its hardness, 
strength, and stiffness. Saw it in two, a third of the distance from one end and 
saw the shorter piece in two, lengthwise. Compare the 
structure at different places. Find rough elevations on the 
outside for the attachment of muscles, and small openings 
into the bone for the entrance of blood vessels and nerves. 
Make drawings to represent the sections. 

2. Procure a fresh bone from a butcher shop. Note 
the difference between it and the dry bone. Examine the 
materials surrounding the sides and covering the ends. Saw 
through the enlarged portion at the end and examine the red 
marrow. Saw through the middle of the bone and observe 
the yellow marrow. 

The ends of the bones are capped by a layer 
of cartilage which is elastic, while the remaining 
surface is covered by a dense sheath of connective 
tissue, called the periosteum. Usually the central 
part is hollow, being filled with a fatty substance, 
known as the yellow marrow. Around the mar- 
row cavity the bone is very dense and compact. 
The red marrow, whose relation to the red cor- 
puscles has already been noted (p. 10), is found 
in the spongv tissue at the ends. 

Fig. 24. Section of a °" 

long bone. i. Marrow The Minute Structure of the bone can 

cavity. 2. Compact tissue. # . 

3. ceiiuiar tissue. 4. Car- ]. studied onlv bv the aid oi a compound micro- 

tilage. 5. Attached hga- *- <- 

ments and tendons. 6. g(»0"ne. 
Periosteum. A 




--6 




THE SKELETON. 95 

Observation. Prepare a section of bone for microscopic study, as fol- 
lows : With a jeweler's saw cut as thin a section of bone as possible. Place this 
between two good-sized whetstones ( having not too much grit ) , cover with water, 
and rub until thin enough to allow the light to pass through. The section may 
then be wet with water and examined under a cover glass, or it may be mounted 
in hard balsam and kept indefinitely. Such sections are most satisfactory when 
prepared from bones that are thoroughly dry, but which have not begun to decay. 
Prepare and study both transverse and longitudinal sections, making drawings. 

Such a microscopic study shows two kinds of small canals which 
penetrate all portions of the bone. These are known as the Haversian 
canals and the canaliculi. The Haversian canals are larger than the 
canaliculi, extend the long way of the bone, and each is surrounded by 
several thin layers, or liminae, of bone substance. The canaliculi ex- 
tend from the Haversian canals at right angles toward a great number 
of irregular clusters in the bone layers, called the lacunae. These, to- 
gether with the canaliculi, present an appearance under the microscope 
similar to that of a number of large burs fastened together by their pro- 
jecting spines. The walls of the lacunae are hard and dense, but 
within each is an open space. In this lies a flattened nucleated body 
that sends branches into the canaliculi. This is the bone cell, or bone 
corpuscle, as it is sometimes called. The chief work of the bone cell 
seems to be that of depositing mineral matter in the walls surround- 
ing it. 

How the Bone Cells are Nourished. The bone cells, like 
all the other cells of the body, are nourished by the lymph that escapes 
from the blood. This reaches the cells in the different parts of the 
bone in two ways, as follows: 

1. The cells at the surface of the bone receive lymph from the 
blood vessels in the periosteum. It comes to them through the cana- 
liculi passing from the outside of the bone to the lacunae near its 
surface. 

2. The cells within the bone receive nourishment through the 
channels penetrating it. Many of these are large enough to be seen 
with the naked eye and inclose small veins and arteries ; others, such 
as the Haversian canals, contain capillaries. The canaliculi convey 
lymph from the capillaries to the bone cells. 

The Plan and Purpose of the Skeleton. The plan of 
the skeleton is such as to provide a framework for a movable struc- 
ture. Obviously the different parts of the body cannot be secured 
to a foundation, as are those of a stationary building, but must be 






ELL [EXT& 



arrange, ffca I plan dial is idueive to motion. A moving struc- 
ture, as a wagon or a bicycle, has within it some strong central part 

■ which the remainder L= joined. The same is true of the skeleton. 

nrl " which the others are joined consists of a long bon 

The skull, the ribs, and the pelvic bones 

are attached directly to the spinal column, while the other parts are 

attached indirectly. The arrangement of all the parts is such that the 

:j! column is made the central, cohering portion of the skeleton 

ir": ::".»•: :_ "If ~L:-r "-'•:■:>-. 

Bone Groups. Very few mmes :f the body can be regarded 
Lstinct ".due in themselves. Each bone, however, is 

■ ■ ■■:- :: ;.:~ir _: v -z:. ::^~ - :.:".: _ .fs :: ~ -- ;"":*"•" se ~~ _::.. "'.:■: 
group serve- The individual bones must not, therefore, be studied 

_ - but wit h reference to the groups to which they belong. The 

more important groups are as : - 
lows 

The spinal column, which 
consists of twenty-four similarly 
shaped bones, one placed above the 
other, called vertebrae.* in addition 
- - — groups of fused vertebrae 
found at the lower end. This 
group supplies the central axis for 
the body, supports the head and 
upper extremities, and incloses and 
protects the spinal cord. The up- 
per seven vertebrae form the neck 
and are called the cervical verte- 
brae. They are smaller and have 
greater freedom of motion than the 
others. The two upper cervicals 
are specially modified to support 
the head and to provide for its 
-ments. The next twelve ver- 
tebrae, in order below the cervical, 
are the thoracic. They form the 
back part of the framework of the 
little fre 

rical TCitebia consists of a lie - - laped portion in front, called 




THE SKELETON. 97 

motion. The five below the thoracic are known as the lumbar verte- 
brae. They are large and strong but admit of considerable motion. 
At the lower end of the column five vertebrae are fused together, 
forming a wedge-shaped bone, called the sacrum. To the sacrum is 
attached a group of from two to four small vertebrae, more or less 
fused, called the coccyx. 

2. TJi-e skull, which is formed by the close union of twenty-two 
irregular bones. For purposes of study, the skull is divided into the 
cranium and the face. The cranium consists of eight distinct bones, 
and incloses the cranial cavity which holds the brain. The face- 
group, consisting of fourteen bones, provides supports for the parts- 
of the face and supplies a movable part (the inferior maxillary) 
w^hich aids in mastication. 

3. The thorax, which contains twenty-four bones of similar 
form, called ribs, and a straight, flat bone, called the sternum, or breast- 
bone. The framework of the thorax is formed by the union of the 
ribs with the spinal column behind and the sternum in front. As 
already stated (p. 33), the ribs are so arranged that the volume of 
the thorax is varied by their elevation and depression, enabling the air 
to be drawn into and forced from the lungs. 

4. The shoulder and pelvic girdles, which form two bony sup- 
ports at the upper and lower portions of the trunk and serve for the 
attachment of the arms and legs. The shoulder girdle is formed by 
four bones — the two clavicles, or collar-bones and the two scapulae, or 
shoulder-blades. The clavicle on each side articulates with the upper 
end of the sternum and serves as a brace for the shoulder, while the 

the body, which is connected by two lateral extensions with a posterior portion 
called the neural arch. The body and the neural arch together completely encir- 
cle a round opening which is a part of the canal that contains the spinal cord. 
From the neural arch are seven bony projections, or processes, three of which 
serve for the attachment of muscles and ligaments, while the other four, two 
superior and two inferior, are for interlocking the vertebrae with each other. 

The different vertebrae are joined together in the column as follows: Be- 
tween the bodies of the several vertebrae are disks of elastic cartilage, each of 
which is about one-fourth of an inch in thickness and is attached firmly to the 
vertebrae above and to the one below. In addition to these, the projections from 
the lower portion of the neural arch of each vertebra fit into the indentations 
of the neural arch over which it is placed and the two are firmly bound together 
by ligaments. To further secure one bone upon the other, numerous ligaments 
pass from vertebra to vertebra, on all sides of the column. 

7 



98 ELEMENTS OF PHYSIOLOGY. 

scapula forms a socket for the humerus aud furnishes many places for 
the attachment of muscles. 

The pelvic girdle is formed, by two large bones which are very 
irregular in shape and are called the innominate bones. They con- 
nect behind with the lower part of the spina] column, called the sa- 
crum, and in front they connect, through a small pad of cartilage, with 
each other. On the inside they present a smooth basin-shaped sup- 
port for the contents of the abdomen, but on the outside are rough and 
uneven and provide many prominences for the attachment of muscles 
and ligaments. Each innominate bone provides a deep, round socket 
into which the femur of the leg accurately fits. 

5. The arm and hand groups. A long bone, the humerus, con- 
nects the arm with the shoulder and gives form to the upper arm. In 
the forearm are two bones, the radius and the ulna, which connect at 
one end with the humerus and at the other, with the bones of the 
wrist. 

A group of eight small rounded bones are found in the wrist. 
These, known as the carpal or wrist bones, are arranged in two rows 
which are movable upon each other. Five straight bones, the meta- 
carpals, connect with the bones of the wrist and form the frame-work 
of the hand. The bones of the fingers and thumb connected with the 
metacarpals, are called phalanges. 

The great number of bones found in the fingers, hand, wrist and 
forearm and the manner in which they are joined, permit great free- 
dom of motion and enable the hand to be used in a variety of ways. 

6. The leg and foot groups. These correspond in form and ar- 
rangement to the bones of the arm and hand. Since, however, the leg 
and foot form special organs of locomotion, certain differences are to 
be expected. The patella at the knee has no corresponding bone in 
the arm ; and the carpus, or ankle, which corresponds to the wrist, 
contains seven instead of eight bones. The bones of the feet and toes 
are the same in number as those of the hand and fingers, but they differ 
greatly in form and size and have less freedom of motion. The femur 
which gives form to the thigh is the longest bone of the body. The 
tibia, or the shin bone, and the fibula, a slender bone, give form to the 
lower part of the leg. 

Note. — To obtain clear ideas of the form and function of the 
bones, careful examination of a prepared and articulated skeleton is 
necessary. Many of the bones, however, may be located and their 



TEE SKELETON. 



99 



general form made out from the living body. For descriptions of 
bones consult some work on anatomy. The different groups of bones 
are shown in figure 25 and named in Table III. 

TABLE III. THE PRINCIPAL BONES AND THEIR GROUPING IN THE BODY. 



I. Axial Skeleton. 



A. Skull, 28. 



1. Cranium, 8. 

a. Frontal, forehead 1 

b. Parietal 2 

c. Temporals, temples 2 

d. Occipital 1 

e. Sphenoid 1 

f . Ethmoid 1 

2. Face, 14. 

a. Inferior Maxillary I 

b. Superior Maxillaries 2 

c. Palatine, palate 2 

d. Nasal bones 2 

e. Vomer : . . 1 

f. Interior Turbinated 2 

g. Lachrymals 2 

h. Malars, cheek bones 2 

3. Bones of the Ear, 6. 

a. Malleus , 2 

b. Incus 2 

e. Stapes 2 



C. 



D. 



Spinal Column, 26. 

1. Cervical, or neck vertebrae. 7 

2. Dorsal, or thoracic vertebrae 12 

3. Lumbar vertebrae 5 

4. Sacrum . . 1 

5. Coccyx 1 

Thorax, 25. 

1. Ribs 24 

2. Sternum. . . 1 

Hyoid, 1 1 



Note — The hyoid, since it forms 
an arch similar to the lower jaw, is 
more properly classed as a bone of the 

skull. 



II. Appendicular Skeleton. 



A. 



B. 



Shoulder Girdle, 4. 

1. Clavicle, collar bone. . 2 

2. Scapula, shoulder blade 2 

Upper Extremities, 60. 

1. Humerus 2 

2. Radius 2 

3. Ulna 2 

4. Carpals, wrist bones . ., ... 16 

5. Metacarpals . 10 

6. Phalanges, of the fingers 28 



C. Pelvic Girdle, 2. 

1. Os innominatum 2 

D. Lower Extremities, 60. 

1. Femur, thigh bone ... 2 

2. Tibia 2 

3. Fibula 2 

4. Patella, knee cap 2 

5. Tarsals, ankle bones 14 

6. Metatarsals, bones of the 

instep .10 

7. Phalanges, of the toes 28 



Adaptation to Special Needs. When any single bone is 
studied in its relation to the other members of the group to which it 
belongs or with particular reference to its purpose in the body, its 
adaptation to some particular place or use is at once apparent. It is 
seen that some bones like the humerus, are adapted to giving form, 
strength, and stiffness to certain parts, while others, like the pelvic 
L.ofC. 



100 ELEMEXTS OF PHYSIOLOGY. 

bones, are fitted for supporting and protecting organs. Others, as 
the wrist and ear bones, are suited to giving a peculiar kind of motion, 
and still others, such as the ribs, are adapted to a variety of purposes. 
The differences that appear among the bones, such as size, structure, 
form, and surface, are but the conditions necessary to adapt them to 
particular forms of service in the body. 

Articulations. 

Any place in the body, where two or more bones meet is called an 
articulation, or joint. Such places are necessary both for the different 
movements of the body and for the development of the skeleton. 
Articulations are divided with reference to their freedom of motion 
into movable, slightly movable, and immovable joints. 

Most of the immovable articulations are found in the skull, 
where the projections of one bone interlock with those of another and 
the two are firmly united by a layer of connective tissue. 

The best examples of joints that are slightly, but not freely mov- 
able, are found in the spinal column. Cartilaginous pads are found 
between the bodies of the vertebrae and these, because of their elas- 
ticity, permit of a slight bending of the column in all directions. 
These movements are secured, not by having one bone glide over the 
other, but by a compression of the cartilage which is relieved by a 
change of direction of the motion. 

Structure of Movable Joints. By far the most numerous and 
important joints of the body are those that admit of motion. Their 
construction is such that the motion occurs easily and without friction. 
At the same time they are strong enough to endure great strain with- 
out dislocation of their parts. The mate- 
rials employed in their construction, besides 
the bones, are chiefly connective tissue, car- 
tilaginous tissue, and synovial membrane. 

At the joints the bones are usually en- 
larged and have specially formed projections, 
or depressions, which fit into corresponding 
depressions or elevations, on the bones with 
which they articulate. In addition to this 
the articular surface is quite smooth and 
dense, having no Haversian canals, and is 
of F a1oint 6 : G i en Ligimems Ctur 2 e covered with a layer of cartilage. Strong 
SynovTaTmembra C n a e rtilage ' 4 ' ligaments pass from one bone to the other 




TEE SKELETON. 101 

to hold each in its place. Some of these consist simply of bands, 
arranged with reference to the form of the joint, while others form 
continuous sheaths around the joints. 

The interior of the joint, except upon the articular surfaces, is 
lined by a form of serous membrane, called the synovial membrane. 
This secretes a thick, viscid liquid, called the synovial fluid which pre- 
vents friction. The membrane passes completely around the joint and 
connects with the ends of the bones to form a closed sac in which the 
fluid is retained. Fig. 26. 

Observation. Procure from the butcher shop the joint of some small animal 
( hog or sheep ) . Cut it open and locate the cartilage, synovial membrane, and 
ligaments. Observe the smoothness of the rubbing parts and the strength of the 
ligaments. 

The Different Kinds of Movable Joints are designated as 
ball and socket, hinge, pivot, condyloid, and gliding. 

In the ball and socket joint, the ball-shaped end of one bone fits 
into a cup-shaped cavity in the other bone, called the socket. The 
best examples are the hip and shoulder joints. This joint admits of 
motion in all directions. 

In the hinge joint the bones are grooved and fit together after the 
manner of a hinge. Hinge joints are found at the elbows and knees 
and also in the fingers. The hinge joint gives motion in but two 
directions — backward and forward. 

A pivot joint is formed by the fitting of a pivot-like projection 
of one bone into a ring-like receptacle of a second bone, so that one, 
or the other, is free to turn. A good example of the pivot joint is the 
junction of the radius with the humerus. The pivot joint admits of 
motion around an axis. 

The condyloid joint is formed by the fitting of the ovoid end of 
one bone into the elliptical cavity of another bone. Examples of such 
are the knuckle joints and the joint of the wrist with the radius and 
ulna. 

Gliding joints are formed by the articulation of plane surfaces. 
Examples of these are found in the articulations between the bones in 
the wrist and ankle. They are the simplest of the movable joints and 
enable one bone to glide upon the surface of another. 

Hygiene. The efficiency of the body as a machine may be greatly 
impaired by lack of adjustment between its parts. If one part inter- 
feres with another, causing, for example, the compression of a blood 



102 ELEMENTS OF PHYSIOLOGY. 

vessel or a nerve, disturbances arise that prevent the perfect function- 
ing of the parts concerned. Since the skeleton serves as a frame- 
work for the body, the other parts are adjusted with reference to it. 
Any disturbance, therefore, of the natural position of the bones is 
likely to interfere with the adjustment of other parts as well. 
Particularly is this true of the spinal column, which serves both as a 
central axis and as a container of the spinal cord. A stooped position, 
or the peculiar lateral curve often assumed in writing, if long con- 
tinued, leads to- permanent distortion of the cartilaginous pads and 
causes an unnatural curvature of the spine. This, in turn, may throw 
important muscles, nerves, and blood vessels out of their natural posi- 
tions. The habit of sitting and standing erect should, therefore, be 
formed early in life. 

There is danger in childhood of bending the long bones of the 
body by improper use. Children who are made to walk before the 
bones have become stiff enough to support the weight are likely to 
bend the bones of the legs, causing the familiar "bow-legs." If 
children are made to sit on benches or chairs which are too high for 
the feet to reach the floor and which are not provided with supports 
for the feet, the thigh bones may be bent from having to support con- 
tinuously the weight of the feet and lower legs. 

Wholesome, nutritious food seems even more important to the 
development of the bones than to the other parts of the body. Where 
this is lacking a condition, known as "rickets," is frequently induced 
in which the bones become soft and are easily bent. 

A fractured bone always requires the aid of a surgeon and no 
time should be lost in securing his services. In the meantime the 
patient should be placed in a comfortable position and the limb sup- 
ported above the level of the rest of the body. While the fracturing 
of a bone is not a serious mishap, it is necessary that the very best 
skill be employed in setting it. Any failure to bring the ends of the 
bones into their normal relations, leads to permanent alterations and 
interferes with the proper use of the limb. 

Dislocations of the larger joints also require the aid of the sur- 
geon in their reduction, and sometimes in their subsequent treatment. 
Simple dislocations of the finger joints, however, may be reduced by 
pulling the parts until the bones can be slipped into position. 

A sprain is an over-strained condition of the ligaments surround- 
ing a joint and frequently requires very careful treatment, When 



TEE SKELETON. 103 

the sprain is at all serious a physician should be called. Because of 
the limited blood supply to the ligaments, they are very slow to heal 
and the temptation to use the joint before it has recovered is always 
great. Massage* judiciously applied to a sprained joint, by bringing 
about a more rapid change in the blood and lymph is frequently bene- 
ficial both in relieving pain and in hastening recovery. 

Summary. Through the skeleton a suitable framework for a 
movable structure, the body, is provided. This supplies strength and 
stiffness to the different parts and aids in their various movements. 
The skeleton is adapted to its purposes through the number and proper- 
ties of the individual bones, and through the manner in which they 
are connected. The joint is a special device for facilitating motion. 

Review Questions. 1. State the purpose of the skeleton. What is the ne- 
cessity for so many bones in its construction? 

2. How may the per cent of animal and mineral matter in a bone be de- 
termined ? 

3. What properties are given to the bone by the animal matter? What by 
the mineral? 

4. Locate the bone cells. What is their particular use in the bones? 

5. What is the mechanical advantage of having certain bones hollow? 

6. Give the uses of the periosteum. 

7. State the purpose of the Haversian canals. Of the canaliculi. 

8. What part does the spinal column play in the plan of the skeleton ? Give 
its other functions. 

9. Name the different materials used in the construction of a joint and the 
purpose served by each. What is the necessity for joints in the skeleton? 

10. State the necessity for standing and sitting erect. 

11. Account for the peculiar shapes of certain bones, as the ribs, the shoulder 
blades, the lower jaw bone, and the bones of the pelvic girdle. 



* A process of gently rubbing, pressing, and kneading parts of the body with 
the hands. 



CHAPTEK XIV. 

THE MUSCULAR SYSTEM. 

Motion is the most noticeable attribute of the animal body. Not 
only can the body transport itself from place to place, but it is able to 
communicate motion to other bodies and, as we have seen, to carry on 
such internal movements as are essential to the vital processes. To 
provide for motion in the body, three well organized systems are re- 
quired: 1. A system of supporting tissues which collectively form 
the skeleton. 2. A system of contractile elements, called the mus- 
cular system. 3. A system for controlling and co-ordinating the move- 
ments, known as the nervous system. 

While the skeleton and nervous system are made to serve other 
important purposes in the body, the muscular system is applied almost 
exclusively to the production of motion. For this reason it is re- 
garded as the motor system. 

Muscular Tissue forms nearly one-half of the weight of the 
whole body and is, therefore, the most abundant of the tissues. This 
fact in itself indicates the importance of the problem of motion. The 
ability of muscular tissue to cause motion is primarily due to two 
properties — irritability and contractility. Irritability is the power 
of responding to a stimulus, that is, of becoming active when acted 
upon in certain ways. This property, which is especially marked in 
nervous and muscular tissues is due to the delicate organization of 
their protoplasm. Contractility is the property which enables mus- 
cle when stimulated, to draw up, or to become shorter and thicker (a 
condition called contraction) and, when the stimulus is withdrawn, 
to return to its former condition of relaxation. 

Muscular tissue, depending upon the cells which make it up, is 
of three varieties, or types. These are the striated, or striped, muscu- 
lar tissue, the plain muscular tissue, and the muscular tissue of the 
heart. A working group of muscular tissue is called a muscle. 

The reddish muscle found in a piece of beef is a good example of striated 
muscle, while the clear ring surrounding the intestine of a cat (shown by a cross- 

104 



THE MUSCULAR SYSTEM. 



105 



section) and the preparation from the cow's stomach, sold at the butcher shop 
under the name of tripe, are good examples of plain muscular tissue. The heart 
of any animal, of course, shows the heart muscle. 

Structure of Striated Muscle. The cells of the striated 
muscles are slender, thread-like structures, varying in length from 
one-third of an inch to five inches, but having a diameter of less than 
one two-hundredths of an inch. Because of their great length they 
are called fibers. They are marked by a number of dark, trans- 
verse bands, called striations, which seem to divide them into a num- 
ber of sections or disks. A thin, sac-like covering, called the sar- 
colemma, surrounds the entire cell and just beneath this may be seen 
a number of nuclei. Within the sarcolemma are still smaller fibrils 
and a semi-liquid substance, called the sarcoplasm. At each end the 
muscle cell tapers to a point from which the sarcolemma continues as a 
fine thread which, blending with other such threads, connects with 
the main tendon of the muscle. Most of the cells receive, at some 
portion of their length, the termination of a 
nerve fiber which penetrates the sarcolemma and 
spreads out as a sort of disk with several nuclei. 
This forms an important structure, known as the 
end plate. 

Within the muscle the individual cells lie 
parallel and are surrounded with sheaths of con- 
nective tissue which bind them into separate 
bundles. These bundles are again bound into 
larger ones and the whole is surrounded by a sin- 
gle sheath of connective tissue which is called 
the perimysium. Between the parts of the mus- 
cle are numerous blood and lymph vessels and 
many small nerves. 
The striated muscles are connected with the skeleton by white 
glistening cords, or bands, called tendons. The tendons are very 
strong and, by uniting with the periosteum of the bone at one end and 
with the perimysium and the fibrils from the muscle cells at the other, 
form verv secure attachments. 




Fig. 27. Muscle cells. 

1. A striated muscle cell 
with attached nerve fiber. 

2. Non -striated cells. 3. 
Muscle cells of the heart. 



Observation. Place a small muscle fi*om the leg of a frog in a fifty per cent 
solution of alcohol and leave it there for half a day or more. Then cover with 
water, on a glass slide, and, with a couple of fine needles, tease out the small 



106 ELEMENTS OF PHYSIOLOGY. 

muscle threads. Protect with a cover glass and examine with a microscope, first 
with a low and then with a high power. The striations, sarcolemma, and some- 
times the nuclei and nerve plates may be made out in such a preparation. 

The striated muscles in most warm-blooded animals, are reddish 
in color, due to the presence of haemoglobin. They are more or less 
rounded in form and as a rule are attached to the bones of the skeleton. 
For this reason they are called skeletal muscles. As most of them 
are under the control of the will, they are also called voluntary mus- 
cles. When stimulated they contract and relax quickly and with 
great force. 

Structure of Non-Striated Muscles. The cells of non- 
striated muscles differ from those of striated muscles in being shorter 
and decidedly spindle-shaped, and in having a single well-defined 
nucleus. Furthermore, there is a lack of striations, the surface being 
smooth, and the connection with the nerve fibers is less marked. Fig. 
27. They are also much smaller than the striated cells, being less 
than one one-hundredth of an inch in length and one three-thousandth 
of an inch in diameter. 

Observation. Place a clean section of the small intestine of a cat in a 
mixture of one part of nitric acid to four parts of water and leave for four hours. 
Thoroughly wash out the acid with water and separate the muscular layer from 
the mucous membrane. Cover a small portion with water on a glass slide and 
tease out,, with needles, until it is as finely divided as possible. Examine with a 
microscope, first with a low and then with a high power. The cells appear as 
very fine, spindle-shaped bodies. 

In the formation of non-striated muscles the cells are attached to 
each other by a kind of muscle cement to form thin sheets or slender 
bundles. These differ from striated muscles in several particulars. 
They are of a pale, whitish color and are not attached to bones, but 
usually surround hollow cavities and tubes such as the stomach and 
intestines. They are not controlled by the will and contract and 
relax slowly. 

Structure of the Heart Muscle. The cells of the heart com- 
bine the structure and properties of the striated and non-striated mus- 
cle cells and form an intermediate type between the two. They are 
cross-striped like the striated cells and are nearly as wide, but are 
quite short. Each cell has a well defined nucleus, but the sarcolemma 
is absent. Fig. 27. They are placed end to end to form fibers and 
many of the cells have branches by which they are united to the cells 



TEE MUSCULAR SYSTEM. 107 

in neighboring fibers. In this way they interlace more or less with 
each other, but are also cemented together. Muscular tissue of this 
variety seems excellently adapted to the work of the heart, and to this 
organ it is entirely confined. 

The Muscular Stimulus. The inactive condition of a mus- 
cle is that of relaxation. It becomes active, or contracts, only when 
it is acted upon by some external influence, called a stimulus, and 
relaxes as soon as the stimulus is withdrawn. Muscles may be stimu- 
lated either directly or indirectly.* 

In the body, the muscles are stimulated through the nerves 
whose connection with the muscle cells has already been noted. The 
nerves are supposed to transmit waves of force, called nervous im- 
pulses, which cause the contraction. (Chapter XVII.) 

Liberation of Energy at the Muscle. The muscle is a 
.kind of engine that does work by the transformation of potential into 
kinetic energy. Evidences of this are found in part in the changes 
that accompany contraction. Careful study shows that, during any 
period of contraction, oxygen and food material are consumed, waste 
products, as carbon dioxide, are produced, and heat is liberated. 

The blood supply is also such that materials may be carried rap- 
idly to and from the muscles. Blood vessels penetrate them in all 
directions and the capillaries lie very close to the individual cells. 
Moreover, provision is made through the nervous system whereby the 
flow of blood is increased when the muscle is at work. From these 
facts, as well as from the great force with which the muscle contracts, 
one must conclude that the muscle is a transformer of energy — that 
within its protoplasm, chemical changes take place whereby the chem- 
ical potential energy of oxygen and food substances is converted into 
the kinetic energy of motion. 

The Plan of Using Muscular Force in the body is inter- 
esting from a mechanical, as well as from a physiological standpoint. 
Muscles exert force only when they contract. They can pull but not 
push. Hence in the body each muscle must work against some force 
that produces a result directly ■ opposite to that which it produces. 
Some muscles work against the elasticity of certain parts of the body ; 



* If the muscles of a frog, in which the brain has been destroyed, be acted 
upon by a weak electric current, they may be made to contract, either by applying 
the current directly to the muscles or by stimulating the nerves that go to the 
muscles. 



108 



ELEMENTS OF PHYSIOLOGY. 



others 
But 



to some extent against gravity ; and others against pressure, 
in most cases, muscles work against muscles. The striated or 







Fig. 28. Movements at the elbow 
Shore's Physiology for Beginners.) 



skeletal muscles are 
nearly all arranged 
after this plan. As a 
rule a pair of muscles 
is so placed, with 
reference to a joint, 
that one moves the 
part in one direction 
and the other in the 
opposite direction. 
From the kinds of 
motion which they 
produce the skeletal 
muscles are classified 
as follows: 1. Flex- 
Adductors and abductors. 3. Rotators. 4. 



(Modified from Foster and 



ors and extensors. 2 
Radiating and sphincters. 

The flexors bend and the extensors straighten joints; the adduc- 
tors draw the limbs toward the axis of the body and the abductors draw 
them away. The rotators (two kinds) twist and untwist joints; while 
the radiating muscles open and the sphincters close the natural open- 
ings of the body. Fig. 28. 

Work of the Non-Striated Muscles. The non-striated mus- 
cles are found in the walls of the food canal and blood vessels. They 
are present in the trachea and bronchial tubes and also in the skin, 
where they #re attached to the roots of hairs. While they do not con- 
tract so quickly or with so great force as the striated muscles, their 
work is more closely related to the vital processes. They propel the 
food through the alimentary canal, regulate the flow of blood through 
the arteries, and perform other acts of great importance in the main- 
tenance of life. 

Exchange of Muscular Force for Motion. The muscles 
contract with great force, but through short distances. It may be 
easily shown that the longest muscles in the body do not shorten more 
than three or four inches during contraction. To bring about the re- 
quired movements of the body which, in some instances, amount to 
four or five feet, requires that a large part of the muscular force be 



THE MUSCULAR SYSTEM. 109 

expressed as motion. This is accomplished by the attachment of the 
muscles to the bones which serve as levers. 

A Lever may be described as a stiff bar which is used in lifting 
weights. It is made to turn on a fixed point of support, called the 
fulcrum. The force applied to the bar is called the power, and that 
which is lifted is termed the weight. Levers are of three kinds known 
as levers of the first, second, and third classes. These differ in the 
position of the power, weight, and fulcrum. In the lever of the first 
class the fulcrum is between the power and the weight. In the second 
class the weight is between the fulcrum and the power. In the third 
class the power is between the fulcrum and the weight. In all three 
classes the distance between the fulcrum and the power is called the 
arm of the power and the distance between the fulcrum and the weight 
is called the arm of the weight. 

General Uses of Levers. In a mechanical sense, levers have 
three uses, as follows: 

1. To change the direction of motion, that is, to enable a force 
acting in one direction to cause a movement in the opposite direction. 

2. To exchange motion for force; illustrated by a small power, 
acting rapidly through a long distance, to move a great weight slowly 
through a short distance. 

3. To exchange force for motion; illustrated by a great power, 
acting slowly through a short distance, to move a small weight rapidly 
through a long distance. 

Experiments. With a stiff wooden bar, a spring balance, and a wedge- 
shaped fulcrum, show: 

1. The position of the weight, the fulcrum, and the power in the different 
classes of levers and also the weight-arm and the power-arm. 

2. The direction moved by both the power and the weight in the use of the 
different classes of levers. 

3. That when the power-arm is longer than the weight-arm, the weight 
is greater but moves through a shorter distance than the power. 

4. That when the weight-arm is longer than the power-arm, the power is 
greater and moves through a shorter distance than the weight. 

Levers of the Body. In the body a bone usually serves as the 
stiff bar or lever, the muscle is the power, part of the body itself, or 
some object to be lifted, is the weight, while the fulcrum is generally, 
though not always, at a joint. The various body levers serve two main 
purposes : 

1. They change the direction of the motion, that is, they enable 



110 ELI F PHYSIOLOGY. 

zing in one direction to move parts of the body in an oppo- 
-ireetion. 

exchange force for morion, that is, they enable mus 
ng through short distances - move p ■ -_-; »s : tfee - "..rough 

■ EKES 

: the latter is. for reasons already stated, the more 

imp. riant 

Im portant Muscles. Tliere are meau :\ze muscles in the body. 

in size, shape, and plan of attachment, to suit their special work. 
Some of those prominent enough to be distinguished from the exterior of the body 
are as toll 

7 he - m the temple, and the m-isseter. in the cheek. 

:ed to the lower jaw and are the chief muscles of mastication. 
At neck: The stemo-mmsteids which pass between the base of the skull 
and the sternum. They assist in turning die head and may be felt at the front 
:e neck. 

• The biceps on the front side, the triceps behir 

- the upper part of the arm beyond the projection of the shoulder. 
" " • wrm: The flexors of the fingers, on the underside, and the 
: "lie fingers on the upper side. 
_ The ad between the thumb and other part of 

ndL 

The pert -~veen the upper front part of the 

thorax and the shoulder, the rr . etween the back of the shoulders and the 

spine,, the rectus abdominis, passing over the abdomen from above do T ~. 
the erector spinae. found in the small of the I 

- -os: The gluteus maxim us fastened between the lower back pa 
the hip and the upper part of the femur. 

f ~ : <<? leg: The • the large muscle on the 

front of the leg which connects with the knee cap bel m 

- The tibialis anterior on the front side, exterior 
to the tibia, and t&e § m&iv&cne m ius. the larsre muscle in the calf of the leg. This 



-/- ir i ■- ised in the body for increasing the force of muscles. The 

foot in lifting the body on tip-toe appear- ■ :o be an ^iception to 

the rule and to increase the power of the muscle. If. however, the distance the 

e compared to the amount which the muscle shortens, it is found 

_ noved farther than the power. This shows clearly that the 

force of the muscle is not increased. The foot in this movement corresponds more 

lever of the i n which the ankle joint serves as a fulcrum 

T .::. But -mce the earth is immovable r - lifted 

- " r he fulcr. - rt is 

support the weight to be lifted. 



TEE MUSCULAR SYSTEM. Ill 

is the largest muscle in the body, and is connected with the heel bone by the 
tendon of Achilles. 

The use of these muscles- in the body is, in most instances, easily determined 
by observing the results of their contraction. 

The Hygiene of the Muscles is almost expressed in the word 
exercise. It is a matter of every-day knowledge that muscles are de- 
veloped and strengthened by use and that they become weak, soft, 
and flabby through disuse. The fact that lack of exercise leads to dis- 
turbances in the vital processes is not, however, so generally under- 
stood. Voluntary exercise can be directly applied only to the skeletal 
muscles. But through the increased work of these, greater activity is 
required of the involuntary or plain muscles. In this way the vital 
processes such as the circulation and digestion are stimulated. For 
the same reason lack of exercise leads to a weakening of the involun- 
tary muscles and a diminished efficiency of the vital processes. Exer- 
cise may therefore, be regarded as having a two-fold purpose: 1. That 
of building up and keeping in tone the muscular system. 2. That of 
improving the general health. 

That muscular exercise may secure the best results from the 
standpoint of health, a number of conditions should be observed: 1. 
It should never be excessive or carried to the point of exhaustion. 
Severe muscular work is destructive both to the muscular and the 
nervous tissue. 2. It should, if possible, be of an interesting nature 
and taken in the open air. 3. It should be counteractive, that is, call- 
ing into play the parts of the body that have not been used during regu- 
lar work. 4. It should be directed toward the weak rather than the 
strong parts of the body. 5. Where one is already tired from study 
or other work, it should be taken with moderation. 

Summary. Motion is provided for in the body mainly through 
the contractility of muscle cells. These are grouped into working parts 
called muscles which in turn are attached to the movable parts of the 
body. The striated muscles, as a rule, are attached to the skeleton and 
bring about the voluntary movements of the body. -The non-striated 
muscles surround the parts upon which they act and produce the invol- 
untary movements. Both, however, are under the control of the 
nervous system which supplies the necessary stimulus. To increase 
the actual movement of the muscles they are in most instances attached 
to bones which serve as levers and which exchange muscular force for 
motion. 



112 ELEMENTS OF PHYSIOLOGY. 

Review Questions. 1. What different systems are employed in the body 
in the production of motion ? What is the special work of each ? 

2. If muscles could push as well as pull would so many be needed in the 
body ? Why ? 

3. Locate a muscle which works against elasticity; one which works against 
pressure; one which to some extent works against gravity. 

-t. Locate rive muscles that act as flexors; five that act as extensors; two 
that act as adductors: two as abductors; one sphincter: and one radiator. 

5. How does the nervous system control the muscles ! 

6. Give differences in structure between the striated and the non-striated 
muscles. In what respect does heart muscle differ from both. 

7. Give the general uses of the striated muscle in the body. 

What are the proofs of the change of potential into kinetic energy during 
contraction. 

9. What are the parts concerned in the physiological lever 3 

10. What is gained and what is lost by the use of levers of the third class 
in the body? 

11. Why is one able to bite harder with the back teeth than with the front 
ones, when the same muscles are used in both cases ! 

12. Measure the distance from the middle of the palm of the hand to the 
center of the elbow joint. Find the attachment of the tendon of the biceps to the 
radius and measure its distance from the center of the elbow joint. From these 
distances calculate the force with which the biceps must contract in order to sup- 
port a weight of ten pounds on the palm of the hand. 

13. Show how contraction of skeletal muscle aids in the circulation of the 
blood and lymph. 

14. How does the lack of sufficient exercise affect the general health? 

15. Where exercise is taken for its effect on the general health., what con- 
ditions should be observed? Why? 



CHAPTER XV. 



THE SKIN. 



Protective Coverings are found at all exposed surfaces of the 
body. They vary considerably, each kind being adapted to the condi- 
tions under which it serves. The more important ones are the skin 
which covers the entire external surface of the body, the mucous mem- 
brane which lines all the cavities that communicate by openings with 
the external surface, and the serous membrane which, including syno- 
vial membranes, lines all of the closed cavities of the body. Of less 
importance are the numerous connective tissue sheaths and membranes 
that surround different organs and tissues. 

The Skin is one of the most Complex structures of the body and 
has a number of functions in addition to that of protection. It is 

estimated to have an area of from 14 
to 16 square feet and to have a thick- 
ness which varies from less than one- 
eighth to more than one-fourth of an 
inch. It is thickest on the palms of 
the hands and soles of the feet, the 
places where it is most exposed. It is 
made up of two distinct layers — an 
outer layer called the epidermis, or 
cuticle, and an inner layer called the 
dermis, or cutis vera. 

The Dermis which is the thicker' 
and heavier of the two layers, is made 
up chiefly of connective tissue fibers. 
These form a dense network which is 
the essential body of the skin and which 
gives the skin its toughness and elas- 
ticity. Imbedded in the connective 
tissue are numerous blood and lymph vessels, oil and perspiratory 
glands, hair follicles, and nerves. Fig. 29. 
8 113 




Fig. 29. The Skin. A. Hair follicle 
and adjacent structures. 1. Oil gland. 2. 
Touch corpuscle. 3. Muscle. 4. Cells of 
fat. 5. Hair shaft. 6. Blood vessels. 
7. Nerve. B. A perspiratory gland with 
duct opening at the surface. (Connective 
tissue not shown.) 



114: ELEMENTS OF PHYSIOLOGY. 

On the outer surface of the dermis are numerous elevations, called 
papillae. These average about one one-hundredth of an inch in height 
and one two-hundred and fiftieth of an inch in diameter. They are 
most numerous on the palms of the hands, the soles of the feet, and 
the under surfaces of the fingers and toes. At these places they are 
larger and more closely grouped and form the parallel curved ridges 
that are readily seen. Each papilla contains the loop of a blood vessel 
and a small nerve, but many of them, in addition, are crowned with 
special nerve endings, called the touch corpuscles. 

Observation. Examine the palm of the hand with a lens. Note the small 
ridges which correspond to the rows of papillae beneath. In these find small pits 
which are the openings of sweat glands. By counting the number of pits on a 
quarter of a square inch of surface^ estimate the number on the entire palm of 
the hand. 

The Epidermis is much thinner than the dermis. It is made 
up of several layers of cells which are flat and scale-like at the surface, 
but are rounded in form, and are filled with soft, granular protoplasm, 
where it joins the dermis. The epidermis is molded onto the dermis, 
filling up the depressions between the papillae and having correspond- 
ing irregularities. Neither blood nor lymph vessels are found in the 
epidermis, nourishment being derived from the lymph which reaches 
it from the blood vessels in the dermis. Only the part next to the 
dermis is made up of living cells. These are active, however, in the 
formation of new cells which take the place of those that, are worn off 
at the surface. Some of these cells also contain the pigment granules 
which give the skin its characteristic color. The hair and the nails 
are important modifications of the epidermis. 

A Hair is a slender cylinder, formed by the union of epidermal 
cells, which grows from a kind of pit in the dermis, called the hair 
follicle. The oval and somewhat enlarged part of the hair within the 
follicle is called the root, or bulb, and the uniform extension beyond 
the follicle is called the shaft. Connected with the sides of the follicles 
are the oil, or sebaceous, glands. These secrete an oily liquid which 
keeps the hair and cuticle soft and pliable. At the base of the follicles 
are small involuntary muscles whose contraction causes the roughened 
condition of the skin that occurs on exposure to cold. 

A Nail is a tough, horny plate, which grows from a depression 
in the dermis, lined with active epidermal cells, called the matrix. 
The back part of the nail is known as the root, the middle convex por- 



TEE SKIN. 115 

tion, the body, and the front margin the free edge. Material for the 
growth of the nail is derived from the matrix which is richly supplied 
with blood vessels. Cells added to the root cause the nail to grow for- 
ward and cells added to the under surface cause it to grow in thickness. 
The cuticle is joined to the nail around its entire circumference so 
that the covering of the dermis is everywhere complete. 

Observations. 1. Examine the cuticle on the back of the hand and on the 
palm. At what place is it thickest and most resisting? Is it of uniform thick- 
ness over the palm? Try pricking it with a pin at the thickest places to see if 
pain is felt. 

2. Examine a finger nail. Is the free edge or the root the thickest ? Trim 
closely the thumb nail and the nail of the middle finger on one hand and try to 
pick up a pin from a smooth, hard surface. The result indicates what use of the 
nails ? Name other uses. 

3. Examine with a microscope, under a low power, the hair from a variety of 
animals, as the horse, dog, cat, etc., noting peculiarities of form and surface. 

Functions of the Skin. The chief function of the skin is that 
of protection. It is enabled to perform this function by the connective 
tissue of the dermis, the tough non-sensitive epidermis, and the touch 
corpuscles with their connecting nerve fibers. The skin not only 
affords protection from mechanical injuries, but also from the action 
of chemicals and from the oxygen of the air. It also affords protec- 
tion from the infectious disease germs that are everywhere present. 

In addition to its work of protection, the skin serves as an organ 
of excretion (p. 88), and, to some extent, as an organ of absorption. 
It is also the most important organ of touch, or feeling, and is the chief 
agency in the regulation of temperature. 

The Skin as an Organ of Adaptation. Forming, as it does, 
the boundary between the body and its physical environment, the skin 
is perhaps the most important agent through which the body is adapted 
to its surroundings. Evidence of this is found in the great variety of 
influences that are able to act on the nerves in the skin and in the 
changes which the cuticle undergoes on exposure. The most striking 
example of such adjustment, however, is seen in 

The Regulation of Temperature. It is necessary to the 
continuance of life that the temperature of the body be maintained at 
a nearly uniform degree, known as the normal temperature, and which 
is 98.5° F. All are familiar with the voluntary efforts that are 
made through clothing, shelter, etc., to keep warm or cool as circum- 



116 E LEU EX is OF PHYSIOLOGY. 

stances require. These efforts are stimulated by sensations of cold or 

heat which arise at the skin. In addition to this, automatic changes 

- Emulated which enable the skin of itself to act either as a means 

for getting rid of extra heat or for limiting its escape from the body. 

The skin at all times is able to act as a retainer of heat because of 
the presence of fat within the dermis. This being a poor conductor 
of heat, acts as does a layer of clothing to prevent its escape. 

The skin also assists in cooling the body. This it does by the 
radiation of heat from its surface, as from a stove, and by the evapora- 
tion of the perspiration. 

Experiments. 1. Wet the back of the hand with water and move it through 
the air to hasten evaporation. Observe that as the hand dries, a sensation of cold 
is felt. Repeat the experiment, using alcohol or gasoline instead of water, noting 
the difference in effect. Alcohol and gasoline evaporate faster than water. 

2. Wet the bulb of a thermometer with alcohol or water. Move it through 
the air to hasten evaporation. Note and account for the fall of the mercury. 

The above experiments, which show that a liquid in evaporating 
absorbs, or takes up heat, illustrates the body's method of disposing 
of an excess of heat through the evaporation of the perspiration. 

The Control of the Heat-Regulating Processes belong, tc 
the nervous system. By changing the relative sizes of the arteries in 
the skin and the internal organs I p. 19) it is able to vary the amount 
of blood circulating in these places. At the same time it can vary the 
activity of the glands in the skin. Through the shifting of the circula- 
tion and by means of the changes in the activity of the perspi 
glands the temperature is kept practically uniform. Thus : 

A fall in temperature is prevented; first, by diminishing the cir- 
culation in the skin where radiation of heat is rapid and incr- 
it in the internal organs where there is no radiation : and second, by 
diminishing the secretion of perspiration which causes loss of heat 
through evaporation. 

A rise of temperature is prevented; first, by the blood being sent 
in large quantities to the skin where the heat can be radiated: and sc 
ond, by increasing the quantity of perspiration which in turn requires 
more heat for its evaporation. 

Alcohol," - interfering with the nervous control of the eireula- 

auses heat to be wasted at a time when the body should be saving 

it If taken on a cold day. it increases the circulation in the skin and 

causes a feeling of warmth. This fact has given rise to the idea that 

alcohol acts as a heat producer in the body. While doing thi- 



THE SKIN. 117 

slight degree, its main effect is that of a heat dissipator. Arctic trav- 
elers have found that they withstand cold far better when no alcohol 
is nsed. 

The Hygiene of the Skin is nearly all included in the prob- 
lems of keeping it warm and clean. It is kept Avarm by clothing; 
bathing is the method of keeping it clean. 

The clothing should be warm and loose fitting. Woolen goods 
are to be preferred to cotton because, being poorer conductors of heat, 
they afford better protection from cold. But woolen clothing fails to 
absorb the perspiration rapidly from the skin and to pass it to the out- 
side where it is evaporated. This, together with its tendency to irri- 
tate, makes it objectionable for wearing next to the skin. If a thin 
layer of cotton clothing, however, is worn between the woolen clothing 
and the skin, these objections are obviated. 

Bathing. One should bathe often enough to keep clean. The 
frequency will depend upon the season, the occupation of the individ- 
ual, and the nature and amount of the perspiration. As to the kind 
of bath to be taken and the precautions to be observed, no specific 
directions can be given. These must be determined by the health and 
natural vigor of the individual. Care must be exercised at all times, 
however, to prevent too great an exposure of the body during the bath. 

The cold bath has been found to have a beneficial influence on the 
general health beyond its direct effect upon the skin. When taken 
with care as to the length of time and the degree of cold, decided tonic 
effects may be produced on the general circulation and on the nervous 
system. The cold bath, taken just before retiring, is also an excellent 
aid in securing sound sleep during hot summer nights. Danger from 
the cold bath arises through the shock to the nervous system and the 
loss of heat from the body. It is avoided by using water whose tem- 
perature is not too low and by limiting the time spent in the bath. A 
brisk rubbing with a coarse towel should always follow the cold bath. 

Treatment of Skin Wounds. Small skin wounds frequently 
become serious from getting infected by germs or "poisoned." A 
wound should be kept clean and if it shows signs of infection, should 
be washed with some antiseptic solution. Or, it may be washed with 
clean warm water and then covered with some antiseptic ointment of 
which there are a number on the market, 

A solution of carbolic acid in water (three parts of carbolic acid to 
one hundred parts of water) is an excellent antiseptic wash. It may 



118 ELEMENTS OF PHYSIOLOGY. 

be used not only for the cleansing of skin wounds, but also in counter- 
acting the poisonous effects that follow the bites of insects. 

Summary. The skin forms the external protective covering of 
the body and also serves additional purposes. It is the most import- 
ant agency in adapting the body to its physical surroundings as shown 
by the part which it plays in the regulation of temperature. 

Beview Questions. 1. Give an example of each of the protective coverings 
of the body. 

2. Compare the dermis and the epidermis with reference to thickness, com- 
position, and functions. 

3. To what is the color of the skin due? How is color affected by sunlight? 

4. What different kinds of epidermis are found on our bodies ? What kinds 
on the body of a chicken ? 

5. What provision is made in the skin for each of its different functions? 

6. How does perspiration cool the body? 

7. What changes occur in the skin when the body is in danger of becoming 
too warm? When in danger of becoming too cold? 

8. Discuss the necessity for the body's adapting itself to external conditions. 

9. How does alcohol make one feel warm when he is losing heat ? 

10. What precautions should be observed, by one in poor health, in taking a 
bath ? 



CHAPTER XVI. 

PLAN OF THE NERVOUS SYSTEM. 

General View. If all the other tissues of the body were re- 
moved, leaving only the nervous, there would still remain a skeleton 
outline of the body. Observation of such a nerve skeleton shows a 
central axis which is made up of two parts, the 
brain and the spinal cord. From the central 
axis white, cord-like structures emerge and pass 
to different parts of the body. These are the 
nerve trunks, and the smaller branches into 
which they divide are the nerves. The nerves 
also undergo division until they terminate as 
fine threads in all parts of the body. The dis- 
tribution of nerve terminals, however, is not uni- 
form as might be supposed, but the skin and im- 
portant organs, like the heart and stomach are 
the more abundantly supplied. Situated along 
the course of many nerves are small enlarge- 
ments, called ganglia, and from these also small 
nerves emerge. At certain places the small 
nerves and ganglia are so numerous as to form 
a kind of network, or plexus. All these parts — 
brain and cord, nerve trunks and nerves, ganglia 
and nerve terminals — taken together, consti- 
tute the nervous system. Fig. 30. 
Dissection of the Nervous System. For this purpose a half 
grown cat is generally the best available specimen. This should be 
killed with chloroform and secured to a board as in the dissection of 
the abdomen. (P. 53.) 

Open the abdominal cavity and remove its contents, tying the alimentary 
canal where it is cut, and washing out any blood which may escape. Dissect for 
the nervous system in the following order: 

119 




Fig. 30. The nerve skel- 
eton. A. Brain. 1. Cere- 
brum. 2. Cerebellum. 3. 
Medulla oblongata. B. Spi- 
nal cord. C. Sciatic nerve. 



120 ELEMENTS OF PHYSIOLOGY. 

1. Cut away the front of the chest, exposing the heart and lungs. Find on 
each side of the heart a nerve which passes by the side of the pericardium to the 
diaphragm. These nerves assist in controlling respiration, and are called the 
phrenic nerves. Find other nerves going to the different organs in the thorax. 

2. Remove the heart and lungs. Find in the back part of the thoracic cavity 
on each side of the spinal column a number of small "knots" of nervous matter 
joined together by a single nerve. These are the sympathetic ganglia. Where 
the neck joins the thorax, find two sympathetic ganglia much larger than 
the others. 

3. Cut away the skin from the upper side of the shoulder and fore leg. By 
separating the muscle and connective tissue where the leg joins the thorax find 
several nerves of considerable size. These connect with each other, forming a net- 
work called the brachial plexus. From here nerves pass to the thorax and to the 
fore leg. 

4. From the brachial plexus trace out the nerves which pass to different 
parts of the fore leg. In doing this separate the muscles with the fingers and cut 
only where necessary to expose the nerves. Note that some of the branches pass 
into muscles while others connect with the skin. 

5. Remove the skin from the upper part of one of the hind legs and separate 
the muscles carefully until a large nerve is found. This is one of the divisions 
of the sciatic nerve. Carefully trace it to the spinal cord, cutting away the bone 
where necessary, and find the branches where it joins the cord. Then trace it to- 
ward the foot discovering its branches to different muscles and to the skin. 

6. Unjoint the neck and remove the head. Examine the spinal cord where 
exposed. Cut away the bone sufficiently to show the connection between the cord 
and one of the spinal nerves. On one of the roots of the nerve, find a small 
ganglion. 

7. Fasten the head to a small board and remove the scalp. Saw through the 
skull bones in several directions. Pry off the small pieces of bone so as to show 
the upper part of the brain. Study its membranes, convolutions, and divisions. 

8. With a pair of nippers break away the skull until the entire brain can 
be removed from its cavity. Examine the different divisions, noting the relative 
position and size of the parts. 

9. With a sharp knife cut sections through the different parts of the brain 
to show the position of the "gray" and the "white" matter. 

Note. — If the entire class is to examine the same specimen, it is generally 
better to have the dissecting done beforehand and the parts separated and tacked 
to small boards. This will permit of individual examination. Sketches of the 
sciatic nerve, brachial plexus, the general form of the brain, and of sections 
through its different parts should be made by the pupils. 

A dissection of the nervous system, carried out by the aid of the 
microscope in great detail, shows it to be perfectly continuous through- 
out the body and to be made up of different varieties of the same 
structural element. 



PLAN OF THE NERVOUS SYSTEM. 



121 



Divisions of the Nervous System. While the nervous sys- 
tem is everywhere closely connected, it may for purposes of study be 
regarded as made^ up of parts which are more or less distinct from 
each other. The classification generally adopted for this purpose is 
the following : 



( Central 



Nervous 

System. . 



k Peripheral 



Fore-brain — Cerebrum 

( Brain \ Mid-brain 

rPons 
{ y Hind-brain. . I Cerebellum 

[Medulla oblongata 
^ Spinal cord 

/ Dorsal-root ganglia 

\ Sympathetic ganglia 
1 Nerves f Cranial 

serves 1 Spinal 



f Ganglia 



The Central Nervous System. This division of the ner- 
vous system lies within the cranial and spinal cavities and consists of 
the brain and spinal cord. While the brain occupies the cranial 
cavity and the spinal cord the spinal cavity, they connect with each 
other through the large opening at the base of the skull to form a 
single continuous structure. The central division is the more com- 
plicated portion of the nervous system and the part most difficult to 
understand. 

The Brain, which is the largest mass of nervous tissue in the 
body, weighs in the average sized man about 50 ounces and in the 
average sized woman about 44 ounces. It is made up of three parts 

which are named from their positions the 
fore-brain, the mid-brain, and the hind-brain. 
Fig. 31. 

The fore-brain consists chiefly of a single 
part, known as the cerebrum. This comprises 
about seven-eighths of the entire brain and 
occupies all the front, middle, upper, and 
back portion of the cranial cavity, spreading 
over and concealing, to a large extent, the 
parts beneath. It presents a large surface 
vi^nlofthl 1 ?^ 8 A fth ce?i"- covered with ridge-like convolutions, between 
D. um ce?ebd l i i u d m bra E: StfedX wMcn ar e deep but narrow depressions, called 

oblongata. I. The fore-brain. 
II. The hind-brain. 




fissures. The cerebrum consists of two ex- 



122 ELEMENTS OF PHYSIOLOGY. 

actly similar divisions, the cerebral hemispheres, which are separated 
by a deep, longitudinal groove, called the median fissure. 

The mid-brain is a short, rounded, and compact body that lies 
immediately beneath the cerebrum and connects the fore-brain with 
the hind-braiu. 

The hind-brain lies beneath the back portion of the cerebrum and 
occupies the posterior enlargement at the base of the cranial cavity. 
It forms about one-eighth of the entire brain and is composed of three 
parts — the cerebellum, the pons, and the medulla oblongata. The 
cerebellum is a flat and somewhat triangular structure whose upper 
surface fits into the concave under-surface of the back part of the cere- 
brum. It weighs about two ounces. In general form and structure, 
it resembles the cerebrum, but it differs therefrom in being more com- 
pact and in having its surfaces covered by narrow transverse ridges 
that lie parallel to each other. The pons, or pons Varolii, named from 
its resemblance to a bridge, is situated directly in front of the cere- 
bellum and is easily recognized by a circular expansion extending for- 
ward from the cerebellum. It consists largely of the nerve fibers that 
connect with different parts of the cerebellum. The medulla, or 
medulla oblongata, is, properly speaking, an enlargement of the spinal 
cord within the cranial cavity. It is somewhat triangular in shape 
and lies immediately beneath the cerebellum. Its structure is differ- 
ent from that of the cord and it contains important groups of cell- 
bodies, or nerve centers. 

The Spinal Cord averages about seventeen inches in length 
and is about two-thirds of an inch in diameter. It does not occupy the 

entire spinal cavity, but terminates at the 
lower part of the first lumbar vertebra. 
It connects at its upper end with the 
medulla and terminates at its lower ex- 
tremity in a number of large nerve roots 
which are continuous with the nerves of 

Fig. 32. Section of spinal cord at the hips and legs. 

L^Sr^feV^Si^'aS The Peripheral Division of the 

structure. 1. Spinal nerve. 2. Ante- , • i l n <i 

rior roots containing efferent fibers, nervous system includes all the nervous 

3. Posterior roots, containing afferent j> -i , • j ,-, -i -, 

fibers. 4. spinal root ganglion. 5. structures round outside the brain and 

White matter of cord. 6. Gray matter. i rpi • j. £ n • i j 

(Modified from Thornton's Human COrCl. lhese Consist 01 the Cranial and 

the spinal nerves and of various ganglia, 
all of which are connected with the central division. 




PLAN OF THE NERVOUS SYSTEM. 123 

The spinal nerves pass from the spinal cord to different parts of 
the body, leaving the spinal cavity through small openings between the 
vertebra. They consist of thirty-one pairs and each nerve joins the 
cord by two roots — a ventral or anterior root and a dorsal or posterior 
root. On the dorsal root of each spinal nerve is a small ganglion 
which, named from its position, is called the dorsal root ganglion. 

The cranial nerves are those which branch from the brain. There 
are twelve pairs of these and they are numbered in the order in which 
they connect with the under side of the brain. The pair nearest the 
front is called the first pair : the next in order the second pair, and so 
on. Unlike the spinal nerves, the cranial nerves present great varia- 
tion and, because of their relation to the special senses, some of them 
are of particular importance. 

Distribution of the Cranial Nerves. 1. The first pair (Olfactory) are 
the nerves of smell and connect the brain with the mucous membrane of the nose. 

2. The second pair (Optic) connect with the retina of the eye and are the 
nerves of sight. 

3. The third, fourth, and sixth pairs (Motores oculi) connect with the mus- 
cles of the eyeballs and control their movements. 

4. The fifth pair (Trigeminal) connect with the skin of the face, the muscles 
of mastication, the mucous membrane of the mouth, and the front of the tongue 
and have various functions. 

5. The seventh pair (Facial) connect with and control the muscles that give 
expression to the face. 

6. The eighth pair (Auditory) connect with the internal ear and are the 
nerves of hearing. 

7. The ninth pair (Glossopharyngeal) connect with the surface of the back 
part of the tongue and with the muscles of the pharynx. 

8. The tenth pair (Vagus) connect with the heart, larynx, lungs, liver, and 
stomach. 

9. The eleventh pair (Spinal accessory) connect with the muscles of the 
neck. 

10. The twelfth pair (Hypoglossal) connect with the muscles of the tongue. 

The Sympathetic Ganglia are found in different parts of the 
body and vary in size from those which are half an inch in diameter to 
those that are smaller than the heads of pins. The largest and most 
important ones are found in two chains which lie in front and a little 
to either side of the spinal column and reach from the neck to the 
region of the pelvis. The number of ganglia in each of these chains is 
about twenty-four. They are connected by the right and left sympa- 
thetic nerves which pass vertically from one ganglion to the other. 



124 ELEMEXTS OF PHYSIOLOGY. 

In addition to these ganglia, important ones are found in the head 
(outside of the cranial cavity) and in the plexuses of the thorax and 
abdomen. The sympathetic ganglia receive nerves from the central 
nervous system, but connect with glands, blood vessels, and the intes- 
tinal walls through nerves which pass from them. 

Protection of Parts. To shield successfully such delicately 
organized structures as those of the nervous system, requires a variety 
of protective agencies. The nerves and ganglia outside of the brain 
and cord are protected by the sheaths that inclose them and by the 
tissues by which they are surrounded. The larger ones are deep-seated, 
as a rule, and occupy localities that are shielded by the bones. 

The brain and cord require special provisions for their protection. 
In the first place the cavities in which they lie are completely sur- 
rounded by bones which not only shield them from the direct effect of 
physical force, but by their peculiar construction prevent the passage, 
to a large degree, of jars and shocks to the parts within. In the sec- 
ond place, they are surrounded by three separate membranes, as fol- 
lows : 1. The dura, or dura mater, a thick, dense, tough membrane 
which lines the bony cavities. 2. The pia, or pia mater, a thin, 
delicate membrane, containing numerous blood vessels, that covers the 
surface of the brain and cord. 3. The arachnoid, a membrane of 
loose texture, that lies between the dura and the pia. 

Finally, within the spaces of the arachnoid, is a lymph-like liquid 
which completely envelops the brain and cord and which, by acting 
as a watery cushion, protects them from jars and shocks. Thus the 
brain and cord are directly shielded by the bones, by membranes, and 
by the liquid which surrounds them. They are further protected from 
the jars and shocks incident to the movements of the body by the gen- 
eral elasticity of the skeleton. 

The Structural Elements of the nervous system are the nerve 
cells, or neurones.* These differ greatly in form and appearance 
from the other cells of the body and also to a marked degree among 
themselves. The majority of them consist of three distinct parts 
known as the cell-body, the dendrites, and the axone. 



* In 1891 Waldeyer advanced the idea that the nervous system was made up of, 
and its work carried on by, separate and distinct units which were all of the same 
kind. To designate this common nervous element he proposed the term neurone. 
This includes the cell body, the dendrites, and the nerve fiber, and is synonymous 
with nerve cell as the term is used in this book. Waldeyer's idea, known as the 
"neurone theory," has been generally accepted. 



PLAN OF THE NERVOUS SYSTEM. 



125 




—S 



IS 



1. The cell-body has in itself the form of a complete cell and 
was at one time so described. It consists of a rounded mass of proto- 
plasm, containing a well defined nucleus. This protoplasm is similar 
to that of other cells but is characterized by the presence of many small 
granules that are easily stained in the preparation of slides for mi- 
croscopic study. 

2. The dendrites are short extensions from the cell-body. They 
branch as do the roots of a tree and form in many instances a complex 

network of tiny rootlets. Their proto- 
plasm like that of the cell-body is more or 
less granular. The dendrites increase 
greatly the surface of the cell-body, to 
which they are closely related in function. 

3. The axone, or nerve fiber, is a long, 
slender process which connects the cell-body 
with some remote organ or tissue. It was 
at one time thought to be a distinct nerve 
element in itself, but a study of the early 
development of the nerve cell as well as the 
observed continuity of the parts has shown 
it to be an outgrowth from the cell-body. 

The Typical Nerve Fiber, or ax- 
one, is made up of three parts. The inner 
or central part is called the axis cylinder. 
This is the essential part of the fiber and is 
the only part continuous with the proto- 
plasm of the cell-body. Surrounding the 
axis cylinder is a layer of substance, white 
in color and of an oily consistency, known 
as the medullary, or myelin, sheath. On the 
outside and completely surrounding the 
medullary sheath, is a thin layer called the 
primitive sheath, or neurilemma. This is 
made up of a single layer of cells which 
form wide, but separate and distinct bands 
around the fiber. Fig. 33. 

In certain fibers branches pass off at 
intervals at right angles from the main 
part. These by distributing themselves in 



Fig. 33. Parts of a typical nerve 
cell, or neurone. A. Cell body 
with projecting dendrites. B. Nerve 
fiber. C. Fiber termination. D. 
Enlarged portion of fiber, showing 
the axis cylinder and its enveloping 
sheaths. E. Cross section of fiber 
still more enlarged. 



126 ELEMENTS OF PHYSIOLOGY. 

a manner similar to the first, greatly extend the influence of a single 
neurone. 

The fibers vary, among the different cells, from less than one 
one-hundredth of an inch to more than three feet in length. 

Arrangement of the Structural Elements. Neurones 
never exist singly in the body, but are massed together to form the 
active structures of the nervous system. Their general arrangement 
in different parts is as follows : 

1. In simple nerves and ganglia. The nerves contain the 
fibrous portions of the neurones. These lie parallel with each other 
and are embedded in a connective tissue support, called the epineu- 
rium. In the nerve trunks and in the large nerves, the fibers are sep- 
arated into bundles. Somewhere along the course of every nerve are 
to be found the cell-bodies belonging to its fibers. These may form 
one of the various small ganglia of the body or only a part of some 
large ganglion. The simple ganglion is but a cluster of cell-bodies 
and their accompanying structures. 

2. In the brain and cord. These parts are made up of both 
nerve fibers and cell-bodies. They may be regarded as a combined 
mass of nerves and ganglia so dense as to be inseparable from each 
other. The gray matter, observed in sections, consists chiefly of cell- 
bodies while the white matter is made up largely of fibers. In the 
cerebrum and cerebellum the cell-bodies are found mostly in the layer 
of gray matter at the surface. From here the fibers pass through the 
white matter to various places, connecting with other portions of the 
brain surface or with other divisions of the brain and cord. Finally 
certain ones pass, as parts of nerves, to places outside of the cranial 
and spinal cavities. 

In the spinal cord the cell-bodies occupy the central gray column, 
while their fibers pass upward or downward through the white matter 
or extend through the spinal nerves to different parts of the body. In 
the medulla, pons, and mid-brain the cell-bodies are collected into 
groups from which the fibers extend to other parts. 

Connection of the Neurones with Each Other. The 
method of connection of the neurones for their work in the body is 
that of a loose, end-to-end union. The fiber branches of one cell, ter- 
minate among the dendrites of other cells and these in turn send their 
fiber- into the dendrites of other cells. There are thus formed, through 
the contiguous nerve cells, great numbers of continuous nerve paths 



PLAN OF THE NERVOUS SYSTEM. 



127 




^-4£ 



? - 



Diagram of a nerve path 
A. Afferent nerve cell. C 
brain or cord. E. Efferent cell. End organs are found at S and 
M. The arrows show the direction of the nervous impulses. 



Fig. 34. 
muscles. 



connecting the skin with 
Intermediate cell of the 



through the body, which bring all parts of it into connection with the 
brain and cord. Fig. 34. The terminal cells in these nerve chains 

usually connect with 
special contrivances, 
called end-organs, of 
which the touch cor- 
puscles are examples. 
A n interesting 
fact relating to the 
nerve paths from dif- 
ferent parts of the 
body is that they 
cross from one side 
to the other before 
reaching the brain. 
For this reason the 
left side of the brain 
is connected with the 
right side of the body and vice versa — a fact which accounts for an 
injury to one side of the brain causing paralysis on the opposite side of 
the body. Most of the crossing occurs within the medulla. 

Summary. The nervous system is made up of similar struct- 
ural elements called nerve cells or neurones. These are the active 
agents in all parts of the system and connect every portion of the body 
with the central nervous mass, consisting of the brain and cord. As 
a whole the nervous system may be compared to a highly developed 
and very complicated system of telegraphy, in which the nerves cor- 
respond to the wires and the brain and cord to the central stations. 

Review Questions. 1. What different structures are to be seen in a skel- 
eton outline of the nervous system? 

2. Describe briefly the cerebrum, cerebellum, medulla, and spinal cord. 

3. Enumerate the different agencies employed in the protection of the brain 
and cord. 

4. State some of the differences between nerve cells and the other cells of the 
body. 

5. Sketch a complete nerve cell or neurone, and name its parts. 

6. Describe the general arrangement of the neurones in the different divis- 
ions of the nervous system. 

7. Account for the differences in color to be seen in sections of the brain 
and cord. 



CHAPTER XVII. 

WORK OF THE NERVOUS SYSTEM. 

In a complex organism, such as the body, where the work done 
by each part must contribute to the general work of all, there must be 
unity and harmony of action. Each organ must act in the right man- 
ner and at the right time and there must be complete co-operation 
among the organs whose functions are related. The securing of such 
action is termed co-ordination and this is a function of the nervous 
system. Briefly stated the work of the nervous system is to control 
and co-ordinate the activities of the body. 

Properties of Nerve Cells. The two properties of the nerve 
cells upon which their work chiefly depends are irritability and con- 
ductivity. The property of irritability was explained in the study 
of the muscles. (P. 104:.) Xerve cells respond more readily to the 
action of stimuli and are therefore more irritable than are muscle 
cells. Moreover, all the stimuli which cause muscular contraction, 
and others besides, may induce activity of the nerve cells. They are 
by far the most irritable portions of the body. 

Conductivity is the property by which the effect of a stimulus is 
transferred from one part of a nerve cell to another. If any part of 
the nerve cell is acted on by a stimulus, the disturbance which it sets 
up is conducted or transmitted to all other parts of the cell. This 
wave-like spreading of the nervous disturbance is termed 'the nervous 
impulse. 

A third property — that of releasing through oxidation a form of 
energy which may cause or re-enforce the nervous impulse — is fre- 
quently attributed to the cell. While there are many reasons for 
believing in the existence of this property, and it is difficult to ex- 
plain certain activities of the nervous system without it, its actual 
presence is difficult to prove. 

The Nature of the Impulse is that of a wave which starts at 
the place of irritation in the nerve cell and moves through the proto- 
plasm wherever continuous paths for it are found. 

128 



WORK OF THE NERVOUS SYSTEM. 129 

The class of waves to which the impulse belongs is difficult to 
determine. At different times it has been regarded as a current of 
electricity, as a progressive chemical change, as a moving vibration 
like that on a stretched rope, and as a molecular disturbance, accom- 
panied by an electrical discharge. It has been shown to be different 
from the first three types of waves, and the last named theory has but 
recently been proposed.* The velocity of the nervous impulse has 
been shown to be about one hundred feet per second. 

Purpose of the Nervous Impulse. The nervous impulse is 
the means employed for controlling and co-ordinating the different 
parts of the body. It is the stimulus which the nerve cells apply to 
all the active parts of the body, including muscle cells, gland cells, 
and other nerve cells. The impulse seems able to produce two dis- 
tinct effects ; first, to throw resting organs into action and to increase 
the action of organs already at work ; second, to diminish the rate or 
check entirely the activity of organs. Impulses producing the first 
effect are called excitant impulses ; those producing the second, inhibi- 
tory impulses. There is reason, however, for believing that impulses 
produce only the first effect and that the observed inhibitory action is 
but an indirect result of excitant impulses. 

Functions of the Parts of the Nerve Cell. The cell-body 
serves as a nutritive center from which the other parts are supplied 
with nourishment. Proof of this is found in the fact that when any 
part of the cell is separated from the cell-body it dies, while the cell- 
body and the remaining parts continue to live. In addition to this 
the cell-body probably re-enforces the nervous impulse. 

The dendrites serve two purposes: First, they extend the sur- 
face of the cell-body and enable it to absorb a greater amount of nour- 
ishment from the surrounding lymph. Second, they act as receivers 
of stimuli from adjacent cells. 

The special function of the nerve fiber is to transmit the im- 
pulse. By its length, structure, and property of conductivity it is 
especially adapted to this work. The axis cylinder, however, is the 
only part concerned in the transmission. The primitive and medul- 
lary sheaths protect the axis cylinder and, according to some authori- 
ties, serve also to insulate it. 



* Theory of Mathews, 1902. The nature of the nervous impulse is that of a 
wave of temporary coagulation that sweeps along the nerve fiber and gives rise 
to an electrical discharge which is the stimulating agent. 

9 



ELEMENTS OF PHYSIOL' 

Action of Nerve Stimuli. Nerve -ells, like the cells of mus- 

re dependent for their activity upon external stimuli. These. 

in a general way, may be divided into two classes — a class which acts 

upon the nervous system from the outside (external) and a stimulus 

supplied by the nerve cells themselv - 

rhe rxtemal stimuli are of various kinds. They include me- 
chanical foi ~. Tinperature changes, chemical reagents, sound waves, 
ieal currents, and rays of light. They may act upon the body 
from the surface or from within the tissues. Moreover, through the 
connection of a special class of nerve cells with the skin, the mucous 
membrane, and other parts of the body, and through the joining of 
their fiber terminations with small bodies called the sense-organs, the 
whole nervous system is made peculiarly susceptible to the action of 
the various stimuli. In other words, the arrangement is such that 
the nervous system is subjected at all times to stimulation from the 
outside. In this way it is kept, to some degree, continuously active. 

S far as known, the only stimulus furnished by the nerve cells 
is the nervous impulse. An impulse traversing the protoplasm of one 
cell, is able to start new impulses in the cells with which it makes 
connection. The excitation is effected through the dendrites which 
are contiguous with the terminations of the fiber that bears the im- 
pulse. This enables a series of impulses to be produced along a given 
nerve path and causes the effect of an external stimulus to be passed 
to remote parts of the body. The method of transmission, by the 
nerve cells, of the effect of an external agent is finely illustrated in 

Reflex Action. When the nervous system receives a sudden 
and strong stimulus, an immediate response is frequently observed 
in the movement of some part of the body. The jerking away of the 
hand on accidentally touching a hot stove, the winking of th^ 
when suddenly exposed to danger, and the quick movements from 
electrical shocks are familiar examples. Since in many cases the 
effect si ems to be turned back toward the originating cause these 
actions are termed reflex. The part of the nervous system involved in 
simple reflex act: - b si :«wn as follows: 

A live frog from which the brain has been removed, is suspended with its 
feet downward and free to move. If a toe is pinched, the foot is drawn away and 
if dilute acid, or a strong solution of salt, is placed on the tender skin, the feet 
are moved as if to take away the irritating substance. If. however, the spinal 
cord be also destroved.. the movements no longer follow irritations of the skin. 



WORK OF THE NERVOUS SYSTEM. 



131 



The experiment shows that while reflex actions may take place 
independently of the brain they cannot take place independently of 
some part of the central nervous system. 

Reflex Action Paths. Following the course of any nervous 
discharge which results in reflex action, the following divisions are 
easily made out: 1. A pathway reaching from the surface of the 
body, or place of irritation, to the central nervous system. This is 
called the afferent pathway. 2. A pathway through the central 
system. 3. A pathway which leads from the central system to the 
active tissues of the body, known as the efferent pathway. Figs. 34 
and 35. 

The cells which form these pathways, present important differ- 
ences and must be considered some- 
what in detail. 

Kinds of Nerve Cells. The 
cells that convey impulses toward 
the brain and cord are called affer- 
ent cells. The cell-bodies of such 
of these as join the spinal cord, 
are located in the spinal root gang- 
lia. They send out short fibers 
which soon separate into two 
branches — one of which passes to 
the surface of the body, while the 
other enters the spinal cord and 
there separates into an ascending 
and a descending branch. The 
afferent fibers form the greater portions of the posterior roots of the 
spinal nerves.* 

The cells that form the central pathways are called intermediate 
cells. They are similar in form to the efferent cells, but as a rule, 
have shorter fibers. 

The cells that convey impulses away from the brain and cord are 
called efferent cells. Their cell-bodies lie in the gray matter of the 
brain and cord and are well supplied with dendrites. Their fibers are 
long and pass to different parts of the body. Those from the cord 
form the anterior roots of the spinal nerves. Fig. 32. 




Fig. 35. Diagram of 

reflex action pathway. 



: In 1811 Charles Bell discovered that the posterior roots of the spinal nerves 



132 ELEMENTS OF PHYSIOLOGY. 

The Cells of the Sympathetic Ganglia complete the efferent 
pathways to the organs of circulation and the viscera. They also serve 
to extend the influence of the efferent cells over a larger area. For 
example, a single efferent cell, "by its branches, may stimulate a large 
number of the sympathetic cells each of which will, in turn, stimulate 
the cells of muscles or glands. Because of this function the sympa- 
thetic cells, are called distributing cells. Since the direction of 
their impulses is from the central system they are also classed as effer- 
ent cells. 

Order of Stimulation. In any reflex action the parts con- 
cerned are stimulated in a definite order which is as follows : First, 
some external stimulus, acting strongly on their fiber terminals, starts 
impulses in the afferent cells. These pass to the central system and act 
as stimuli to the central or intermediate cells. These, through their 
impulses, now stimulate the efferent cells and they in turn act in the 
same way on the muscles. Fig. 34. 

Purpose of Reflex Action. If the student will carefully note 
and study the reflex actions of his own body for a period, say of two 
weeks or longer, he must conclude that they all serve the common pur- 
pose of protection — that through their agency portions of the body in 
danger are removed to places of safety. Furthermore, the speed with 
which this is accomplished is so great that the position of safety is 
reached before one is aware of the danger. TThile these movements 
are sometimes unnecessary and often fail of their purpose, they must 
be regarded as a protective agency of the greatest importance. 

A Larger View of Reflex Action, however, must be taken. It 
represents the ordinary method of reaction of the involuntary organs, 
proofs of which' are easily found. A case in point is the secretion of 
saliva when food is present in the mouth. The pressure of food 
against the mucous membrane starts the nervous reactions and these 
pa -sing through the medulla, reach and stimulate the salivary glands. 
Again on sudden exposure to cold, the little arteries going to the skin 
quickly diminish in size, check the normal flow of blood to the skin, 
and prevent too great a loss of heat. In this case the nervous reactions, 



contain afferent, or sensory fibers, while the anterior roots contain efferent or 
motor fibers. This discovery showed each spinal nerve to be double in function. 
Tracing the fibers of the posterior roots they are found to be distributed 
chiefly to the skin, while those of the anterior go chiefly to the muscles and to the 
sympathetic ganglia. 



WORK OF THE NERVOUS SYSTEM. 



133 



starting at the surface of the body, have been transmitted through the 
central system and through efferent and sympathetic cells, to the mus- 
cles in the walls of the arteries. Other illustrations of the reflex 
nature of involuntary actions are found in the swallowing of the food, 
and in changes of the blood supply to different organs. 

A fact of even greater importance, however, is that all the activi- 
ties of the body, including the so-called voluntary actions, are in nature 
reflex. By this statement is meant that the primary causes of any and 
all action are to be found outside of the nervous system, that these on 
being impressed upon the nervous system, start the reactions which 
finally reach the organs that give them expression. Ordinarily, how- 
ever, the term reflex is employed in the restricted sense in which it has 
been discussed. 

Voluntary Actions comprise those movements of the body of 
which we are conscious and which seem to be controlled by a certain 
influence designated the will. In some respects they may be regarded 
as a higher order of reflex action, or as reflex actions modified by the 

mind. The specific action of the 
mind in these movements is not under- 
stood. The final result, however, 'is 
to so modify the natural reflexes that 
the effect of a given stimulus cannot 
be foretold. Reactions to produce 
voluntary movements must take place 
through the cerehrum. To this organ 
afferent pathways, from all parts of 
the body, may be traced and from it 
efferent pathways extend, through 
nerve fibers, to all the voluntary mus- 
cles. Fig. 36. 

Automatic Action. Everyday 
experience teaches that any nervous 
reaction becomes easier by repetition. 
A given act performed a number of 
times under conscious direction, estab- 
lishes a nervous condition which en- 
ables the act to occur without such di- 
rection. That is to say, the parts con- 
cerned in causing the act have become automatic, or self-acting. 




Figf. 36. From the eye to the muscles 
in voluntary motion. E. Eye. O A. 
Sight area. MA Motor Area. Sp. Speech 
area. S. Hearing-. Arrows show direc- 
tion of the impulses. 



134 ELEMENTS OF PHYSIOLOGY. 

Within the nervous system are many automatic mechanisms, some of 
which, like the regulation of the heart-beat, are natural, while others. 
as the motion of the hand in writing, have been acquired. 

The development of automatic mechanisms, probably consists in 
the establishment of special reaction pathways in the nervous system. 
Through the branching of the nerve fibers, many pathways are open 
to any given nervous discharge. If, however, the discharge is con- 
stantly guided in a particular path, as in the doing of a specific act. 
this becomes in time the natural outlet, and will be the one followed 
when there is no conscious interference. When this is accomplished. 
it is simply necessary that a given stimulus start the reaction. This 
acting reflexively and following the established pathway, will reach 
the right destination and produce the desired result independently of 
other causes. 

Habits. In addition to the automatic activities that involve 
parts of the body only and relate to specific acts and processes, there 
is a class of automatic activities that involves the body as a whole. 
These are known as habits. Habits are acquired conditions of the 
nervou- system that enable given stimuli to prompt definite and far- 
reaching results. They are also acquired by repetition and. in com- 
mon with other automatic activities, serve the important purpose of 
economizing the nervous energy. However, if pernicious habits are 
formed instead of those that are useful they are detrimental both from 
a physical and a moral standpoint. 

Functions of the Parts of the Nervous System. The rela- 
tionship between the different parts of the nervous system is. as a rule. 
too close to ascribe specific duties to particular divisions. In a general 
way it may be stated: 1. That the gray matter in the spinal cord, 
medulla, pons, and mid-brain are concerned in the reflex actions of the 
different parts of the body. 2. That the cells in all these places, in 
addition to responding to stimuli from the surface of the body, are 
also connected with and are subordinate to nerve cells in the cerebrum 
and cerebellum. 3. That the reflex centers in the medulla, because 
of their controlling influence upon respiration, circulation, and the 
secretion of liquids, are of special importance in the maintenance of 
life. 

Efforts to discover some special function of the cerebellum have 
been, in the main, unsuccessful. Its removal from small animal- in- 
stead of producing definite results usually interferes in a mild way 



WORK OF THE NERVOUS SYSTEM. 135 

with a number of activities. The most noticeable results are a general 
weakness of the muscles and an inability on the part of the animal to 
balance itself. While it seems closely related to the voluntary move- 
ments of the body, its relation to other parts of the nervous system, 
also concerned in these movements, is not understood. 

Functions of the Cerebrum. While the work of the cerebrum 
is also closely related to the work of the general nervous system, it, 
more than any other part, exercises functions peculiar to itself. As 
already noted, nervous reactions that occur through the cerebrum are 
so modified as to lose, in many cases, their apparent relation to external 
stimuli. This power to postpone, or entirely inhibit, nervous reactions 
is but a part of the general work ascribed to the cerebrum as the a organ 
of the mind." Numerous experiments performed on the lower ani- 
mals, together with observations on man, show the cerebrum to be the 
seat of the mental activities and to make possible, in some way, the 
processes of consciousness, memory, volition, imagination, emotion, 
thought, and sensation. 

Localization of Cerebral Functions. Many experiments have 
been made in order to determine whether the entire cerebrum is con- 
cerned in each of its several activities or whether special functions 
belong to different parts. These experiments have been performed 
upon the lower animals and the evidence thus obtained has been com- 
pared with observations made on injured and imperfectly developed 
brains in man. The results have led to the conclusion that certain 
forms of the work of the cerebrum are localized and that some of its 
parts are concerned in processes that are different from those of others. 
In addition to this, the location upon the cerebral surface of the portions 
having to do with motion, vision, speech, and hearing have been rather 
accurately determined. Fig. 36. It must not be inferred from this, 
however, that all the activities of the cerebrum are localized. Further- 
more, the function of much of the cerebrum is still unknown. 

Nervous Control of Important Processes. 

Circulation of the Blood. The ability to contract at regular intervals has 
been shown to reside within the heart itself. Among other proofs is that fur- 
nished by a cold-blooded animal, like the frog, whose heart remains active for 
quite a while after removal from its body. These automatic contractions, how- 
ever, are not sufficient to meet all the demands made upon the circulation. The 
needs of the tissues for constituents of the blood vary with their activity and 



eleme: 

it is therefore necessary to frequently vary the force and rapidity of the heart's 
contractions. Such changes the heart is of itself unable to bring about. 

For the purpose of controlling the rate and force of the heart's contrae- 

- connected with the central nervous system by two kinds of nerves: 

1. Nerves containing fibers that convey excitant impulses to the heart to quicken 

'ion. 2. Xerves containing fibers that convey inhibitory impulses to the 

to slow its motion. 

The cell-bodies of the excitant fibers are found in the sympathetic ganglia, 
but they are connected by fibers with the medulla/ by which they are con- 
trolled. The cell-bodies of the inhibitory fibers are also in the medulla and 
pase : the heart as a part of the spinal accessory and vagus nerves. 

In addition to the fibers above mentioned, are those that convey impulses 

from the heart to the medulla. These act reflexively, when the heart is likely 

to be overstrained, to cause a dilation of the blood vessels which lessens the 

re that the heart must exert to empty itself of blood, and in this way 

serves as a kind of safety valve for the heart. 

Ch a ng es in the rate and force of the heart's contractions can be made to 
correspond only to the general needs of the body. When the blood to a par- 
ticular organ is to be increased or diminished, the muscle in the walls of the 
arteries must be called into play. The arterial muscle is controlled by fibers 
from sympathetic ganglia, which in turn are controlled by fibers from the medulla. 
The action of these muscles in varying the blood supply has already been con- 
sidered. (P. 19.) 

It is thus seen that the control of the circulation belongs to nerve centers in 
the medulla. These centers act reflexively and are stimulated by a number of 
conditions that relate to the movement of the blood through the body. 

Respiration. The respiratory nerves connect the different muscles of respi- 
ration with a cluster of cell-bodies in the medulla, called the respiratory center. 
This together with the nerves and muscles in question, form a self-acting or 
automatic mechanism, similar in some respects to that of the heart. Through 
the impulse s ] _ from the center to the respiratory muscles a rhythmic action 

is maintained sufficient to satisfy the usual needs of the body for oxygen. The 
demand for oxygen, however, varies with the activity of the body and to such 
variations the respiratory center alone is unable to respond. The regulating 
factor of the respiratory movements has been found to be the condition of the 
blood with reference to the presence of oxygen and carbon dioxide. If the 
blood contains much carbon dioxide and little oxygen it acts as a strong stimulus 
to the respiratory center, causing it, in turn, to stimulate the muscles with 
greater intensity and frequency. On the other hand, if the blood contain much 
oxygen and little carbon dioxide.it acts only as a mild stimulus. This explains 
how physical exercise may increase the force and rapidity of the respiratory 
- The muscles at work consume large quantities of oxygen and give much 
carbon dioxide to the blood. In this way they get the blood into such a condi- 
tion that it can act strongly upon the respiratory center. 

The respiratory center is also connected by nerves with the mucous mem- 
brane lining the air passages. Any irritation of the nerves in the membrane 



WORK OF THE NERVOUS SYSTEM. 137 

is transmitted to the respiratory center and this leads to such modifications of 
the respiratory acts as sneezing and coughing. 

There are also centers in the brain which modify the action of the respiratory 
center. This is shown by the fact that one can voluntarily change the rate and 
force of the respiratory acts. 

Digestion of the Food. From the mucous membrane of the alimentary 
canal numerous fibers pass to the medulla. Fibers also pass from the medulla 
to the sympathetic nervous ganglia and to the muscles and glands concerned in 
digestion. Food in the canal, by its pressure against the walls, stimulates the 
fibers in the mucous membrane and these in turn act upon the nerve centers. 
These now stimulate, chiefly through the sympathetic cells, the muscles and glands 
of digestion. In this way the secretions of the various liquids and the move- 
ments of the canal occur with direct reference to the food present to be acted upon. 

Hygiene of the Nervous System. 

The peculiar work of the nervous system requires of it an extreme 
delicacy of structure. For this reason there is no tissue in the hody so 
easily injured as the nervous tissue. This necessitates special provisions 
for protection from physical injuries, such as have already been noted. 
(P. 124.) There is no provision, however, for the protection of the 
nervous system from continued misuse, or direct abuse, on the part of 
the individual. 

The far-reaching effect of nervous disorders is another reason for 
carefully regarding the conditions that make or mar the efficiency of 
the system. Because of its relation to different parts of the body, 
weakness of the nervous system is as frequently manifested through the 
inefficiency of different organs as through well recognized nervous 
symptoms. Poor digestion, irregularities of the heart's action, troubles 
with the eyes, etc., are quite frequently indicative of overtaxed nerves, 
and disappear when they regain their normal condition. 

Mental work is conducive to the vigor of the nervous system. 
Even severe mental exertion may be undergone without bad effect, pro- 
vided proper hygienic conditions are observed. But "brain workers" 
as a class are more or less liable to nervous derangements. For this 
reason they should observe at least the more general rules in caring for 
the nervous system and practice economy in the use of nervous energy. 

Plenty of sleep is one of the first requirements of the nervous sys- 
tem. It is during sleep that the exhausted brain tissues are replen- 
ished. To shorten the time required for sleep is to weaken the brain 
and lessen its working force. No one should attempt to get along with 
less than eight hours of sleep each day and most people require more. 

Fretting and worrying are unhealthful forms of nervous activity 



138 ELEMENTS OF PHYSIOLOGY. 

and should, if possible, be avoided. Certainly the vast quantity of 
nervous energy which is expended in these ways cannot be used in 
useful work. A fretting person may be likened to a leaking steam 
engine. The escaping steam not only lessens the working power of 
the engine but is disagreeable and distracting as well. It should be 
remembered in this connection that worry and not work usually causes 
the mental wreck. 

Physical Exercise properly taken is essential to the nervous 
system both for its direct and indirect effects. A large proportion of 
the nerve cells have for their function the production of motion and 
are called into play only through muscular activity. Physical exercise 
also counteracts the unpleasant effects of mental work. Hard study 
causes an excess of blood to be sent to the brain and a diminished 
amount to other parts of the body. Exercise redistributes the blood 
and equalizes the circulation. Light exercise, therefore, should follow 
hard study. The student before retiring at night is greatly assisted in 
getting to sleep and put in better condition for the next day's work, by 
fifteen or twenty minutes of light gymnastics. 

The nervous system is also benefited through the general effect of 
physical exercise upon the organs of digestion, circulation, and respira- 
tion in causing them to provide a more liberal supply of food and 
oxygen to all the tissues of the body. 

Nervousness. Through excess of mental work, long continued 
anxiety, disorders of the eyes, the use of much tea or coffee, or other 
causes, a weakened condition of the nervous system is frequently in- 
duced which is indicated chiefly by a supersensitiveness to all forms of 
stimuli. This condition, described by the general term, nervousness, 
is not only a source of great discomfort and annoyance but is wasteful 
of nervous energy and a menace to the general health. 

The first step towards securing relief from such a condition should 
be the removal of the cause. At the same time there should be culti- 
vated that condition of mental poise which enables one to resist many 
causes of irritation. Special exercises that have for their aim the 
equalization of the circulation or the strengthening of the blood vessels 
of the neck and the brain also have beneficial effects. 

Nervousness in children often results from the work and worry of 
school life. Frequent examinations, the grading of class recitations, 
nagging on the part of the teacher, and other influences that keep chil- 
dren on a nervous strain are highly injurious, and to them may be 
attributed not a few of the nervous disorders of school days. Such 



WORK OF THE NERVOUS SYSTEM. 139 

school work of course defeats the very aim for which it is intended and 
should be eliminated from all school system as soon as possible. 

Effect of Drugs. Because of its delicacy of structure a num- 
ber of chemical compounds, or drugs, are able to produce injurious 
effects upon the nervous system. Some of these are violent poisons 
while others, in small quantities, are mild in their action. Certain 
ones in addition to their direct physiological effect, bring about modi- 
fications in the nervous system which cause an unnatural appetite, or 
craving, that leads to their continued use. This is the case with 
alcohol,* the intoxicating substance in the usual saloon drinks., and 
with nicotine, t the stimulating drug in tobacco. The same is true of 
such drugs as morphine and chloral and several others that are fre- 
quently used as medicines. This danger of becoming a slave to a use- 
less and pernicious habit should dissuade every one from the use of any 
and all drugs, except in cases of positive emergency. 

The Power of Self-Oontrol should be cultivated as much for 
its effect upon the nervous system as upon the "moral fiber." It is the 
chief safeguard against the formation of bad habits and the only means 
of redemption from such habits that have already been formed. Per- 
sistent cultivation of the power to control the appetites and the passions, 



*The Injurious Effects of Alcohol upon the body, which have been referred 
to at different times, may now be summarized. Alcohol injures protoplasm and 
leads to diseases of important organs, as the liver, kidneys, and stomach; it 
disturbs the nervous and muscular control of the circulation; it interferes 
with the action of the brain; it causes a general weakness of the entire body 
and diminishes its "power of resistance" to attacks of disease; and, besides, 
creates an appetite that is hard to control. While alcohol can be oxidized in 
small quantities in the tissues and, to a limited extent, can supply energy, the 
body has no way of storing it or of regulating its supply to the cells. Its use 
as a beverage is a dangerous practice. Its value as a medicine is a question 
upon which authorities do not agree. 

t Nicotine is an oily, colorless liquid which may be extracted from the 
tobacco plant. Its action on the nervous system is that of a poison. Taken in 
small quantities it is a mild stimulant and, if the doses are repeated, a habit 
is formed which is difficult to break. Tobacco is used mainly for the stimulat- 
ing effects of this drug. While not so serious in its results as the alcohol and 
morphine habits, the use of tobacco is of no benefit, is a continual and useless 
expense, and, in many instances, causes a derangement of the healthy action of 
the body. To the bad effects of the nicotine, may be added those of questionable 
substances added by the manufacturer, either for their agreeable flavor or for 
adulteration. 

The use of tobacco by the young is especially injurious, as it interferes with 
the proper development of both body and mind. The cigarette, which has so 
many consumers among small boys, has done no end of harm and every effort 
should be made to prevent its use. 



140 ELEMENTS OF PHYSIOLOGY. 

as well as all forms of activity that may injure the body or the higher 
nature, gives a power and tone to the nervous system that raises the in- 
dividual to a higher plane of life. Moreover, it is the necessary condi- 
tion for the exercise of deliberate choice in supplying the needs of the 
body. 

Fainting, attended with or without loss of consciousness, is 
caused by an insufficient supply of blood to the brain. The usual rem- 
edy is to lay the patient on his back with the head slightly lower than 
the rest of the body and make provisions, if necessary, for fresh air. A 
little cold water may be dashed in the face and strong ammonia, or 
smelling salts, applied to the nostrils. The clothing should be loosened 
around the neck and chest and where the condition is prolonged, artifi- 
cial respiration should be applied. 

Summary. The nervous system is able to control and co-ordi- 
nate the different organs of the body through its intimate connection 
with all parts and through a stimulus (the nervous impulse) which it 
supplies and transmits. Nervous reactions, originating from the effects 
of external stimuli, follow definite paths and lead to activity of differ- 
ent parts of the body. All such reaction pathways are through the 
central nervous system. In voluntary action the reaction is through 
the cerebrum — a condition that leads to important modifications in the 
results. The cerebrum is the organ of the mind. The other divisions 
of the nervous system are so closely related that' their special work can 
scarcely be separated from the general work of the nervous system. 

Review Questions. 1. Give the function of each of the parts of the 
nerve cell or neurone. 

2. Give the nature and purpose of the nervous impulse. 

3. What arrangements are to be found for exciting impulses in the different 
nerve cells? 

4. Describe a reflex action and show how it is brought about. 

5. Distinguish between afferent, efferent, and intermediate cells. 

6. State the purpose of the sympathetic cells. 

7. How do reflex actions protect the body? In what sense are all of the 
actions of the body reflex? 

8. How does voluntary action differ from reflex action? 

9. How does automatic action lessen the work of the nervous system? 

10. Why are habits hard to change? Show the importance of forming 
useful habits. 

11. Discuss the relation of mental work, sleep, exercise, and the use of 
drugs to the vigor of the nervous system. 

12. How does the cultivation of the power of self-control strengthen the 
nervous system ? 



CHAPTER XVIII. 

PRODUCTION OF SENSATIONS. 

Impulses of afferent nerve cells serve two purposes. They lead to 
motion in different parts of the body and they stimulate activity within 
the cerebrum. Cerebral activity is of different kinds, the most elemen- 
tary being called sensations. The term is used here in a technical sense 
and sensations must not be confused with the nervous impulses on the 
one hand or with the secondary cerebral effects, called emotions, on the 
other. They are properly regarded as the immediate effects of afferent 
impulses on the brain and as the first stage in the series of mental proc- 
esses that these impulses may arouse. 

In some way not understood the brain is able to refer the sensa- 
tion to the part of the body at which the impulses originate. Pain, for 
example, is felt not at the brain, where the sensation is produced, but 
at- the injured part. This act of the brain is known "as localizing the 
sensation. " 

Classes of Sensations. Perhaps as many as twenty distinct 
sensations such as pain, touch, hunger, etc., are recognized. If these are 
studied with reference to their origin, it will be seen that part of them 
arise by the action of well defined stimuli upon special contrivances, 
known as the sense organs, while the others, as a rule, arise from in- 
definite stimuli upon parts of the body that do not possess sense or- 
gans. The first class, and this includes the sensations of touch, tem- 
perature, taste, muscular sensations, smell, hearing, and sight, are 
known as special sensations. The other class, which includes the sen- 
sations of pain, hunger, thirst, nausea, comfort, discomfort, and those 
due to disease, are known as general sensations. 

Purpose of Sensations. Sensations indicate within the brain 
conditions that exist outside of it. By means of special sensations the 
physical conditions surrounding the body are made known and through 
the general sensations the brain is impressed with the state of the va- 
rious organs within the body. In this way sensations provide the neces- 

141 



142 ELEl >F PHYSIOL' 

sary conditions for intelligent and purposeful action on the part of vol- 
untary organs. Furthermore, since - ns supply the onk basis 
for knowledge of any kind, the so-called ""mental life" is entir- 
pendent upon them. Without sensation, there can be no thought. 

The Steps in the Production of Sensations are not essen- 
tially different from those in the production : reflex ~::n. First : 
all. external stimuli act on the fiber terminations in the sense orga:: 5,01 
elsewhere, starting nervous impulses in different cells which pass 
some part of the central nerv os system. The reaction then passes 
through the cells of the central system to the part of the cerebrum 
which gives rise to the sensation. Thus, the final response to the stim- 
instead of being the contraction of a muscle, or the secretion of a 
gland, is an activity of the cerebrum. 

In the production of any special sensation the following parts are 
concerned : 

1. A sense organ where the termination of the afferent eel"- is 
acted upon by the stimulus. 

The part of the brain which gives rise to the sensation. 
A chain of nerve cells which transmits the reaction from the 
sense organ to the brain. 

Sense Organs may be regarded as special receivers of the nerv- 
os s imuli. Their purpose, in all instances. : ; ~ sause the stimulus to 
act to the best advantage on the terminations of the nerve cells with 
which they are in close connection. It may be inferred, therefore, that 
the construction of any sense organ will have special reference to the 
nature of the stimulus which it is to receive. 

Simple Forms of Sense Organs. ILf -i:^-~-: : :-.._. : 
sense : _ n is one found among various tissues. It consists of the ter- 
minal branches of a nerve fiber spread over a small area among the cells, 
as a network or plexus. Such endings are very numerous in the skin 
and muscles. 

Next in order of complexity are the end-bulbs. Th— sst of 

rounded, or elongated, connective tissue capsules within which nerve 
fibers terminate. On the inside the fiber 1 - - -heath and divides 
into branches which wind around through the substance of the capsule. 
End-bulbs are abundant in the lining membrane of the eye. called the 
conjunctiva. They are also found in the skin of the lips and in the 
asues around the joints. 

Slightly more complex than the end-bulbs, are the touch-corpus 



PRODUCTION OF SENSATIONS. 143 

the chief sense organs in the skin. They are elongated, bulb-like 
bodies, having a length of about one three-hundredth of an inch and are 
composed chiefly of connective tissue. Each corpuscle receives the 
termination of one or more nerve fibers. These, on entering, lose the 
medullary sheath, and separate into a number of branches which pene- 
trate the corpuscle in all directions. The touch corpuscles are found 
chiefly in the papillae of the dermis. Fig. 29. 

Pacinian Corpuscles. These are the largest of the simple forms 
of sense organs and are easily seen with the naked eye. They lie along 
the course of nerves in many parts of the body and have the general 
form of grains of wheat. The Pacinian bodies are composed of con- 
nective tissue arranged in separate layers around a narrow central cav- 
ity, called the core, which contains the termination of a large nerve 
fiber. They are found in the connective tissue beneath the skin, along 
the tendons, around joints, and among the organs of the abdominal 
cavity. 

Observation. Spread out the mesentery of a cat and hold it between the 
eye and the light. Pacinian corpuscles will be seen in the form of small trans- 
lucent bodies. Secure a portion of the mesentery over a circular opening in a 
thin piece of cork and examine it with the microscope with a low power. Follow 
the course of the nerve fiber to the nerve from which it branches. 

The simple forms of sense organs have a more or less general dis- 
tribution over the body and are concerned in the production of three 
special sensations. These are touch, temperature, and the muscular 
sensation. 

Touch, or feeling, is the simplest of the special sensations. The 
sense organs employed are the touch corpuscles and their stimulus is 
some form of pressure, or impact. Pressure applied to the skin, by 
acting on the fiber terminations within the corpuscles, starts the im- 
pulses which pass to the brain. It is found that change of pressure, 
rather than pressure that is constant, is the active stimulus. That sen- 
sations from different parts of the skin vary, is shown by the following 

Experiment: Place the points of a pair of dividers on the back of the 
hand of one who looks in the opposite direction. Is one point felt or two? 
Repeat several times, changing the distance between the points, until it is fully 
determined how near together the points must be placed in order to be felt as one. 
In like manner test other parts of the body, as the tips of the fingers and the 
back of the neck. Compare the results obtained at different places. 



144 ELEMENTS OF PHYSIOLOGY. 

Temperature Sensations are limited almost entirely to the skin. 
They are of two kinds which are designated as heat sensations and cold 
sensations. Whether the temperature sense organs are different in 
structure from the touch corpuscles is not known. It is known, how- 
ever, that the same corpuscles do not respond alike to heat, cold, and 
pressure. 

Experiment. Slowly and evenly draw a blunt pointed piece of metal over 
the back of the neck. If it be of the temperature of the skin, only touch sensa- 
tions will be experienced. If it be a little colder (the temperature of the room) 
sensations cf cold will be felt at certain spots. If slightly warmer than the 
body, heat sensation spots will be found on other parts of the skin. If the hot 
and cold sensation spots be marked and tested from day to day. they will be 
found to remain constant as to position. 

A change of temperature, rather than any specific degree of 
heat or cold, is the active temperature stimulus. The sensation of 
warmth is obtained when the temperature of the skin is being raised, 
and of cold when the temperature of the skin is being lowered. Hence, 
sensations can indicate only in a relative way the actual temperature of 
objects. 

Muscular Sensations refer to impressions which are produced 
by impulses arising at the muscles. These originate at the fiber ter- 
minations which are found in both the muscles and their tendons. By 
muscular sensations one is conscious of the location of a contracting 
muscle and of the degree of its tension. They also make it possible to 
judge of the weight of objects. There is doubt, however, of the accu- 
racy of classifying these as special sensations. 

The Sense of Taste. The sense organs of taste are found 
chiefly in the mucous membrane covering the upper surface of the 
tongue. If this surface be examined, a number of rounded elevations, 
or large papillae, will be found. Toward the back of the tongue two 
rows of these, larger than the others, converge to meet at an angle, 
where is located one of exceptional size. Surrounding each papilla is 
a narrow depression within which are found the sense organs of taste, 
called the taste buds. Each bud contains a central cavity which com- 
municates with the surface by a small opening — the gustatory pore. 
Within the cavity are many slender spindle-shaped cells from which 
hair-like projections, at one end, extend toward the gustatory pore 
while they terminate, at the other end, in short fibers. Branches from 
the nerves of taste enter at the inner end of the taste bud and spread out 



PRODUCTION OF SENSATIONS. 145 

between the spindle-shaped cells. These find their way to the brain as 
parts of two pairs of cranial nerves : those from the front of the tongue 
joining the trigeminal nerve and those from the back of the tongue, the 
glossopharyngeal nerve. 

The gustatory stimulus is some chemical or physical condition of 
substances which is manifested only when they are in a liquid state- 
For this reason only liquid substances can be tasted. Solids, to be 
tasted must first be dissolved. 

The different taste sensations are described as bitter, sweet, sour, 
saline, and alkaline, and in the order named are recognized as the tastes 
of quinine, sugar, vinegar, salt, and soda. As to the manner in which 
these different tastes are produced, little is known. Flavors such as 
vanilla and lemon, and the flavors of meats and fruits are really smelled 
and not tasted. 

The Sense of Smell. The sense organs of smell are found in 
the mucous membrane lining the upper divisions of the nasal cavities. 
Here are found two kinds of cells in great abundance — the columnar 
epithelial cells, and the cells which are recognized as the sense organs of 
smell. The latter are spindle-shaped, having at one end a slender 
thread-like projection which reaches the surface and, at the other end, a 
fiber which joins the olfactory nerve. In fact the olfactory cell resem- 
bles closely a nerve cell, and is thought to be a nerve cell by many 
authorities. 

The divisions of the olfactory nerve pass through many openings 
in the ethmoid bone of the skull and connect with the olfactory lobes of 
the cerebrum. 

The Olfactory Stimulus. Only substances in the gaseous state 
can be smelled. From this it is inferred that the stimulus is supplied 
by the movements of the gas particles. Solids and liquids are smelled 
by means of the gas particles which they exude. It is also necessary 
that the odoriferous substance be kept moving through the nostrils and 
that it come in contact with the olfactory cells. 

Sight and Hearing. The sense organs of sight and hearing, 
which are highly complicated structures, are considered in the chap- 
ters following. 

Summary. Sensations are activities of the cerebrum that have 
reference to conditions found either within the body or outside of it. 
They are excited by afferent impulses and are necessary for the intelli- 
10 



146 ELEMENTS OF PHYSIOLOGY. 

gent and purposeful action of the voluntary organs and for acquiring 
knowledge. General sensations indicate conditions of the various 
organs of the body while special sensations, as a rule, denote conditions 
external to the body. The sense organ is a device for enabling the 
stimulus to act to the best advantage on the afferent nerve cells in start- 
ing the impulses. 

Review Questions. 1. Compare sensations and reflex actions with refer- 
ence to their nature and cause. 

2. How do general sensations differ from special sensations? 

3. Of what value is pain in the protection of the body.' 

4. Of what value are the feelings of comfort and discomfort in the care of 
the body? 

5. "\Yhat different kinds of sense organs are found in the skin? 

6. Through Avhat sense avenues is one made aware of the presence of solids, 
liquids, and gases? 

7. State the purpose of the sense of smell: of taste. 



CHAPTER XIX. 

THE LARYNX AND THE EAR. 

General Facts Relating to Sound. If some sonorous body, as 
a bell be struck, it is given a quivering, or vibratory, motion which it 
imparts to the substances with which it comes in contact. These take 
up the movements and pass them to objects more remote, and they in 
turn give them to others, until a very considerable distance is reached. 
Such moving vibrations, or waves, constitute the external stimuli of the 
organ of hearing and are called sound waves. Sound waves always 
originate in vibrating bodies. Their usual mode of progress is through 
the air which, because of its lightness, elasticity, and abundance easily 
receives impressions from vibrating bodies and transmits them in all 
directions. While these movements are correctly classified as waves, 
they bear little resemblance to the familiar waves on water. Instead 
of being made up of crests and troughs they consist of alternately con- 
densed and rarefied portions that have been caused by the backward and 
forward movements of the vibrating particles. They also pass through 
the substances that transmit them in all directions from the point of 
origin, instead of spreading like water waves over a surface. In the 
sound waves, as in all other waves, however, it is only the wave form 
that moves forward, the individual particles that make it up simply 
vibrating back and forth. 

Any sound wave represents a small but definite amount of energy 
which is a part of the original force that acted on the vibrating sub- 
stance. When they strike against bodies they are, therefore, able to 
exert a small amount of force which, under favorable circumstances, is 
capable of setting the bodies into vibration. It is because of this fact 
that sound waves may be employed as nervous stimuli. 

Sound waves are transmitted by solids and liquids as well as by 
air. They may be re-enforced by suitable contrivances such as sound- 
ing boards and air columns. The pitch or height of a sound, depends 
upon the rapidity of the vibrations of the sonorous body. The inten- 

147 



14S ELEMENTS OF PHYSIOLOGY. 

sity or energy of a sound depends primarily upon the force applied to 
the sonorous body. 

Simple Experiments. I. To illustrate the origin of sound, (a) Strike 
a bell an easy blow and hold some light substance, such as a pith ball attached 
to a thread, against its side, noting result, (b) Sound a tuning fork by strik- 
ing it against a table. Test it for vibrations as above. (c) Pluck a string 
of a guitar, or violin, and find proofs that it is vibrating while producing sound. 

2. To show transmission of sound. Vibrate a tuning fork and press the 
stem against a table or desk. The vibrations will be perceived in all parts of 
the room. Xow press the stem lengthwise against a small block of wood, and, 
after setting it in vibration, lower the block into a tumbler of water which is 
resting on the table. This sound will also reach to all parts of the room. 
Observe that to reach the ear the vibration from the fork must pass through 
a solid, a liquid, and the air. 

3. To show effects of sound waves. While holding a thin piece of paper 
against a comb with the lips, produce musical tones with the vocal cords. The 
paper will be set into vibration by the sound waves, producing the so-called 
'•comb music." " 

•4. Re-enforcement of sound, (a) Vibrate a tuning fork in the air noting 

feebleness of tone produced. Then hold the stem against a door or the top of a 

table, noting the difference, (b) Hold a vibrating tuning fork over a tall jar 

or bottle and gradually add water. A depth will be reached when the air in the 
vessel re-enforces the sound. 

The Value of Sound Waves from a physiological standpoint 
is not easily overestimated. They indicate the condition of one's sur- 
roundings, as regards rest or motion, and give warning of approaching 
danger. They comprise the chief means of communication between 
man and his fellows and, in the sphere of music, provide one of the most 
elevating forms of entertainment. The existence of two instruments of 
sound in the body — one for the production, the other for the detection 
of sound — is certainly suggestive and emphasizes the ability of the 
body to adapt itself to, and make use of, its physical environment. 
Both of these instruments are constructed with special reference to 
the nature and properties of sound waves. 

The Larynx. 

The Sound-Producing Mechanism of the body consists of the 
following parts : 

1. Delicately arranged bodies which are easily set into vibration. 

2. An arrangement for supplying the necessary force for making 
them vibrate. 



THE LARYNX AND THE EAR. 149 

3. Contrivances for modifying the vibrating parts so as to pro- 
duce changes in pitch and intensity. 

4. Parts which re-enforce the original vibrations. 

5. Organs by means of which the sound waves are converted into 
the forms of articulate speech. 

The central organ in this complex mechanism is the larynx. 

The Larynx, which forms a part of the air passages (p. 31), is a 
short tube situated immediately above the trachea. Mucous membrane 
lines the inside and small muscles cover most of the outer surface. 
The framework is made up of cartilage. At the top it is partly encir- 
cled by a small bone (the hyoid), and its opening into the pharynx is 
guarded by a flexible lid, called the epiglottis. While the cartilage in 
the walls is in eight separate pieces, the greater portion of the structure 
is formed by two pieces only — the thyroid cartilage and the cricoid 
cartilage. Bott of these can be felt in the throat; — the former as trie 
projection known as "Adam's apple/' and the latter as a broad ring a 
little below. 

The thyroid cartilage consists of two Y-shaped pieces, one on 
either side of the larynx, meeting at their points in front and each ter- 
minating at the back in an upward and a downward projection. Between 
the back parts of the thyroid is left a space which is occupied chiefly by 
the larger portion of the cricoid cartilage. The latter has the shape of 
a signet ring, and is so placed that the part corresponding to the signet 
fits into the thyroid space while the ring portion encircles the larynx 
below the thyroid. Muscles and connective tissue pass from one car- 
tilage to the other at all places save one, on each side, where the down- 
ward projections of the thyroid form hinge- joints with the cricoid. This 
joint permits of the motion of either cartilage upon the other. 

At the top of the cricoid on each side is a small triangular piece, 
called the arytenoid cartilage. Each arytenoid is movable on the cri- 
coid and is connected with one end of a vocal cord. 

The Vocal Cords consist of two narrow strips of tissue 
which, connecting with the thyroid cartilage in front and the 
arytenoid cartilages behind, lie in folds of the mucous membrane. 
Above the vocal cords, and resembling them in appearance, are two 
other folds of the membrane called the false vocal cords. The open space 
between the "true" cords is called the glottis. When sound waves are 
not being produced the glottis has a triangular form due to the spread- 
ing apart of the arytenoid cartilages and their attached cords. But 



150 ELEMENTS OF PHYSIOLOGY. 

when in use the cords are made to approach each other until the glottis 
is only a narrow slit. 

The Location of the Larynx, in the air passage, enables the 
expiratory muscles to be used as accessory organs in the production of 
the voice. By the force which they are able to give to the air passing 
from the lungs, the cords are set into vibration. During the produc- 
tion of vibrations the natural expulsion of the air is checked bv the 
partial closing of the glottis and it is held back in the lungs. It is then 
forcibly expelled against the cords. 

To Produce the Voice a special set of muscles draws the aryte- 
noid cartilages toward each other, bringing their margins very near 
and parallel to each other. In this position they are easily set into 
vibration by blasts of air from the lungs. Changes in pitch are caused 
by varying the tension of the cords. This is accomplished by tilting the 
thyroid cartilage in such a way that the upper portion moves away from 
the arytenoids. These changes are indicated by movements of the 
larynx and may be easily observed if the finger is pressed against it, 
between the thyroid and the cricoid cartilages, while the musical 
scale is being sung. The distance between them diminishes in ascend- 
ing the scale and increases in descending the scale. 

In the production of tones of very high pitch, the vibrating por- 
tion of the cords is thought to be actually shortened by the margins 
being drawn into contact at the back. 

The intensity of the voice is governed by the force with which 
the air is expelled from the lungs. The vibrations of the cords are also 
greatly re-enforced by virtue of the peculiar structure of the upper air 
passages, which act as resonance tubes. 

In the production of speech the mouth is recognized as the chief 
organ in modifying the vibrations of the vocal cords. Its movements 
during speech are quite significant and may be studied with profit. 
The "vowels" are more nearly the pure vibrations of the cords while the 
"consonants" are largely modifications produced by the tongue, teeth. 
and lips. Ordinarily speech is carried on without change in pitch. In 
whispering the vocal cords do not vibrate. 

Observations. 1. Lightly grasp the larynx with the fingers while talking. 
Observe the changes both in the position and shape of the larynx in the produc- 
tion of different sounds. 

2. Observe the difference in the action of the muscles of respiration in the 
production of loud and faint sounds. 



TEE LARYNX AND TEE EAR. 



151 



3. Pronounce slowly the vowels, A, E, I, 0, U, and the consonants, C, F, 
K, M, R, S, T, and V, noting the shape of the mouth, the position of the tongue, 
and the action of the lips in each case. 

The Ear. 



The Sense Organ of Hearing is a contrivance for enabling 
sound waves to act as sensory stimuli. • In the performance of its func- 
tion it receives, transmits, and concentrates the waves on a suitable ex- 
posure of nerve cells. It includes three parts — the external ear, the 
middle ear, and the internal ear. 

The External Ear consists of the part on the outside of the 
head called the pinna, or auricle, and the tube leading into the middle 
ear called the auditory canal. The pinna by its peculiar shape aids to 
some extent the entrance of sound into the canal. The auditory canal 
is a little more than an inch in length and one-fourth of an inch in 
diameter and is closed at its inner end by a thin membrane, called 
The Membrana Tympani. This membrane consists of three 
thin layers. The outer layer is a continuation of the lining of the au- 
ditory canal ; the inner, is a part of the membrane of the middle ear ; 

while the middle is a layer 
of connective tissue. Being 
thin and delicately poised, 
the membrana tympani is 
easily made to vibrate by the 
sound waves which enter the 
auditory canal. 

The Middle Ear, or 
tympanum, is an irregular 
cavity in the temporal bone, 
lined with mucous mem- 
brane and connected with 
the pharynx by a slender 
canal known as the eu- 
stachian tube. It is also 
filled with air. Extending 
across the middle ear and connecting with the membrana tympani, 
on one side, and with a membrane closing a small passage to the 
internal ear, on the other, is a chain of three small bones. These 




Fig. 37. Diagram of the organ of hearing. A. 
Auditory canal. B. Membrana tympani. C. Mid- 
dle ear with a chain of bones. D. Semi-circular canal. 
E. Auditory nerve. F. Cochlea. G. Eustachian 
tube. (Reduced from Rettger's Advanced Lessons in 
Physiology.) 



152 ELEMENTS OF PHYSIOLOGY. 

named in their order from the membrane are, the malleus, the incus, 

and the stapes. Where the malleus joins the membrane is a small mus- 
cle whose contraction has the effect of tightening the membrane. The 
eustachian tube admits air freely to the middle ear, providing in this 
way for an equality of atmospheric pressure on the two sides of the 
membrane. The chain of bones transmits vibrations from the mem- 
brana tympani to the internal ear. 

In the transmission of vibrations across the middle ear an actual 
concentration of wave force occurs in the following manner : 1. The 
chain of bones, being attached to the walls of the middle ear. fomis a 
lever of the second class in which the malleus is the long arm and the 
incus and the stapes, the short arm, their ratio being about that of 
three to two. 2. The area of the membrana tympani is about twenty 
times as great as that of the internal ear which is acted upon by the 
stapes. 

From this arrangement it follows that the force exerted by the 
stapes where it joins the internal ear is thirty times as great as that 
exerted on each corresponding area of the membrana tympani. In 
other words this arrangement enables the force of a sound wave upon a 
relatively large surface to be concentrated upon a surface which is rela- 
tively small. 

The Internal Ear, or labyrinth, occupies a series of irregular 
canals in the petrous process of the temporal bone of the skull. (P. 
99.) It is very complicated in structure but at the same time, very 
small. Its greatest length is about three-fourths of an inch and its 
greatest diameter not more than one-half inch. It consists of three 
main parts — the vestibule, the semi-circular canals, and the cochlea. 
It is double throughout, being made up of an outer portion which lies 
next to the bone and completely surrounds an inner portion of the same 
general form. The outer portion is surrounded by a membrane which 
serves as periosteum to the bone and. at the same time, holds the liquid 
belonging to this part, called the perilymph. The inner portion called 
the membranous labyrinth, consists essentially of a closed membranous 
sac filled with a liquid, called the endolymph. and contains the termina- 
tions of the auditory nerve. 

The Vestibule is the central portion of the internal ear and is 
somewhat oval in shape. It is in communication with the middle ear 
through a small opening in the bone called the fenestra oralis, at which 
place the stapes is in contact with its outer membrane. Six different 



THE LARYNX AND THE EAR. 153 

openings lead off from the vestibule at different places. The largest 
of these forms the main canal of the cochlea. The other five form 
the different openings into 

The Semi-Circular Canals. These canals, three in number, 
pass through the bone in three different planes. One extends in a hori- 
zontal direction and the other two vertically, but each lies at right 
angles to the other two. Both ends of each canal connect with the vesti- 
bule, though two of them join by a common opening. The inner mem- 
branous labyrinth is continuous through each canal and is held in posi- 
tion by small strips of connective tissue. 

The Cochlea is the part of the internal ear directly concerned in 
hearing. It consists of a coiled tube which makes two and one-half 
turns around a central axis and bears a close resemblance to a snail 
shell. It differs from a snail shell, however, in being made up of 
three separate canals, lying side by side. These are named the scala 
vestibula, the scala tympani, and the scala media. Any vertical sec- 
tion of the cochlea will show all three of these divisions. (Fig. 37.) 

The Scala Vestibula and the Scala Tympani appear in 
cross section as the larger of the cochlear canals. The former, so 
named from its connection with the vestibule, occupies the upper posi- 
tion in all parts of the coil. The latter lies below at all places and is 
separated from the channels above partly by a margin of bone and 
partly by a membrane. It receives its name from its connection with 
the middle ear or tympanum. Both the scala vestibula and the scala 
tympani belong to the outer portion of the internal ear and are filled 
with the perilymph. At their upper ends they communicate with 
each other by a small opening. 

The Scala Media lies between the scala vestibula and the scala 
tympani and is separated from each by a membrane. It is a part of the 
membranous portion of the labyrinth and is filled with the endolymph. 
It receives the terminations of fibers from the auditory nerve and may 
be regarded as the true sense organ of hearing. The nerve fibers ter- 
minate upon the membrane which separates it from the scala tympani, 
called the basilar membrane. This extends the length of the cochlear 
canal and is stretched between a projecting margin of bone on one 
side and the outer wall of the cochlea on the other. It is covered 
with a layer of well-formed cells, some of which have small, hair-like 
projections and are known as the hair-cells. Above the membrane 
and resting partly upon it, are two rows of rod-like bodies, called 



154 



ELEMEXTS OF PHYSIOLOGY. 



i\6 Gv> 



the rods 0/ Cor//. These, by leaning toward each other, form a kind 
of tnnne] beneath. They number more than 6,000 and form a con- 
tinuous series along the margin of the membrane. 

How We Hear. The sound waves which originate in vibrating 
bodies are transmitted by the air to the external ear. The pinna and 

the auditory canal direct 
the waves against the 
membrana tympani and 
this is made to vibrate. 
By the chain of bones 
the vibrations are car- 
ried across the middle 
ear and communicated to 
the liquid in the laby- 
rinth. From here the 
vibrations pass through 
the channels of the coch- 
lea and set into vibra- 
tion different portions 
of the basilar membrane. 
This serves as stimulus 
to the fibers of the audi- 
tory nerve which trans- 
of hearing to the brain. 




Fig. 3$. Path of the 
(Diagrammatic.) 



sound wave through the ear. 



mits the impulses that cause the sensation 
Fig. 38. 

Much of the peculiar structure of the cochlea is not understood. 
Its minute size and its location in the temporal bone make its study 
extremely difficult. The connection of the scala tympani with the 
middle ear is supposed to furnish an outlet for the vibrations, thereby 
preventing echoes. The rods of Corti are thought to act as dampers 
on the basilar membrane, to prevent the continuance of vibrations 
when once thev are started. 



Theories of Hearing. The basilar membrane,, while continuous throughout, 
may be regarded as made up of many separate cords of different lengths stretched 
side by side. Any given tone is able to set into vibration only those cords which 
sustain a fixed relation to the wave length in question. Thus, a tone of one 
pitch sets one portion of the membrane into vibration and has no effect on the 
other parts. This theory, which is based 'upon our knowledge of sympathetic 
vibration, was proposed by Helmholtz. 






THE LARYNX AND THE EAR. 155 

Another theory is that the entire basilar membrane responds to all vibrations 
and that the analyses of sound takes place in the brain. 

A third view is that the filaments from the hair cells, rather than the basilar 
membrane, respond to the vibrations and stimulate the terminal branches of the 
nerve cells. This view* is based on a comparative study of the development of 
the so-called hair cells in a large number of the lower animal forms. 

The Purpose of the Semi-Circular Canals is not under- 
stood. There is, however, much evidence for the belief that they act 
as sensory organs for balancing the body. Their removal or injury 
does not, affect the hearing but does interfere with the ability to keep 
the body in an erect position. 

Care of the Ear. The ear, being a delicate organ, is fre- 
quently injured by careless or rough treatment. The removal of ear 
wax by the insertion of pointed instruments has been found to inter- 
fere with the natural method of discharge and to irritate the mem- 
brane. It should never be practiced. It is unnecessary in the 
normal ear to cleanse the auditory canal proper, as the wax is passed 
to the end of the canal, by a natural process, where it is easily re- 
moved. If the natural process is obstructed, clean warm water and 
a soft linen cloth may be employed in cleaning the canal without 
liability of injury. Clean warm water may also be introduced into 
the ear as a harmless remedy in relieving inflammation of the audi- 
tory canal and the middle ear. Children's ears are easily injured 
through rough handling and it goes without saying that their ears 
should never be boxed or pulled. 

It sometimes happens that a plug of wax gets lodged in the ear 
and closes the canal so completely as to cause temporary deafness. 
Such plugs are easily removed and the hearing restored by the phy- 
sician and, both in the case of painful disturbances and in the gradual 
loss of hearing, he should be consulted. 

Summary. Through the larynx and the ear, sound waves are 
utilized by the body in different ways but chiefly as a means of com- 
munication. The larynx produces sound on the principle of a reed 
instrument which is re-enforced and modified by the air passages. 
The ear supplies suitable conditions for the action of sound waves 
upon nerve cells. Both are constructed with special reference to the 
nature and properties of sound waves and illustrate the body's ability 
to adapt itself to, and make use of, its physical environment. 



"Investigations by Ayers on "The Vertebrate Ear.' 



ELEMENTS OF PHYSIOLC 

Review Questions. 1. Describe a sound wave. How does it originate? 
How is it transmitted! State its effect on delicately poised bod: — 

2. How do sound waves differ from the wares on the surface of wa: 

3. How may sound waves be re-enforced? 

4. Describe the plan for the production of sound waves in the body. 

5. Account for the variations of pitch and intensity in sounds produced by 
the organ of the voice. 

6. How is the sound produced by the vocal cords changed into speech? 
What parts of the organ of hearing are concerned in transmitting sound 

wav^- 

B. Give purpose of the middle ear. 

9. Trace a sound vibration from a bell to the basilar membrane and the 
impulses it causes from there to the brain. 

10. Describe the membranous labyrinth. 

11. Give directions for the proper care of the ear. 



CHAPTER XX. 

THE EYE. 

Light Waves. The stimulus for the sensation of sight, called 
light, is supposed to consist of vibratory movements, or waves, of 
various lengths. These differ from sound waves in form, velocity, 
origin, and method of transmission. Light waves are able to pass 
through a vacuum showing that they are not dependent on the dif- 
ferent forms of matter for transmission. They are supposed to be 
transmitted by what the physicist calls ether, a highly elastic and 
exceedingly thin substance which fills all space and penetrates all 
matter. As a rule light waves originate in bodies that are highly 
heated, being started by the vibrations of the minute particles of 
matter, called molecules. 

The path of a light wave is determined by various conditions. 
Within a medium of uniform density it is transmitted in a straight 
line and with unchanging velocity. If it enters a rarer medium, its ve- 
locity increases : if a denser medium its velocity diminishes ; and if 
it enters any of these media from any direction except perpendic- 
ularly, it is turned in its course, or refracted. If it strikes against 
some body lying in its course, it may be thrown off (reflected) , or 
it may enter the body and be either transmitted through it or ab- 
sorbed. In the latter case the force is spent in raising the tempera- 
ture of the object. 

Waves of light striking against the smooth surface of a mirror 
are thrown off in definite directions, depending on the angle at which 
they strike the mirror. (Illustrate by holding a mirror in the direct 
rays of the sun.) But light waves which strike rough surfaces are 
reflected in all directions and apparently without reference to the 
angle at which they strike. (Illustrate by placing a piece of white 
paper in the direct rays of the sun. It matters not from what direc- 
tion it is viewed, intense rays of light from it strike the eye.) This 
kind of reflection, known as diffusion, plays a very important role in 

157 



158 ELEMENTS OF PHYSIOLOGY. 

rendering objects visible. Light from the sun, for example, when it 
strikes aifferent objects on the earth is reflected from them in all di- 
ns. These reflected waves enable objects to act as independent 
sources of light and to become visible. 

Formation of Images. Images are produced by light waves 
when they represent to the eye the form of the object from which they 
If. for example, a convex lens is moved backward and for- 
ward between a candle and a screen in a poorly lighted room, a posi- 
tion will be discovered where the form of the candle falls on the 
screen. This picture of the candle is called its image. 




'.'-:-■£ 



_ Fig 39. Formation of images. On the right by a simple convex lens. On the left by the eve. 
The candle flame represents a luminous, or light-gnrim j, oody, while light passes from the arrow by 



The explanation is as follows : The light of the candle comes 
from great numbers of separate and independent points in the flame. 
The lens, by its peculiar shape, refracts the separate waves so that 
Eh se i-oming from any given point in the candle are brought to a 
corresponding point on the screen. Furthermore, the images of points 
on the screen occupy relations to each other similar to those in the 
candle. Thus the area of light on the screen has the form of the 
candle flame and may be called its image. The same explanation 
applies if j instead of the luminous candle, a body that simply re- 
tx Light, as a book, is used. 

In figure 39. trace the different light waves from their points of origin, at the 
candle or arrow, to their points of convergence on the screen or retina. Account 
for the fact that the image? are inverted. 

Experiments Illustrating the Simple Properties of Light. 1. Heat an 
iron or platinum wire in a clear gas flame. Observe that when a high tempera- 
ture is reached it gives out light or becomes lumin - 

2. Cover one hand with a white and the other with a black piece of cloth 



THE EYE. 159 

and hold both for a short time in the direct rays of the sun. Note and account 
for the difference in temperature which is felt. 

3. Stand a book, or a block of wood, by the side of an empty pan in the 
sunlight, so that the end of the shadow falls on the bottom of the pan. Mark the 
place where the shadow terminates and fill the pan with water. Account for 
the shadow's changing in length. 

4. Place a coin in the center of an empty pan and let the members of 
the class stand where the coin is barely out of sight over the edges of the 
pan. Fill the pan with water and account for the coin's coming into view. 

5. Hold a piece of cardboard, about eight inches square and having in 
the center a smooth, round hole an eighth of an inch in diameter, in front of a 
lighted candle in a darkened room. Back of the opening place a muslin or paper 
screen. Look for an image of the candle on the screen. Account for the fact 
that it is inverted. Hold a convex lens between the cardboard and the screen 
so that the light passes through it also. The image should now appear smaller 
and more distinct. 

The Sense Organs of Sight consist of the two eyeballs and 
their accessory parts. Each is located within a cavity of the skull 
bones, called the orbit, where it is held in position by suitable tissues 
and turned in different directions by a special set of muscles. A cup- 
like receptacle is provided within the orbit by layers of fat and a 
smooth surface is supplied by a double membrane that lies between 
the fat and the eyeball. In front the eyeballs are protected by mova- 
ble coverings, called the eyelids. These are composed of dense layers 
of connective tissue, covered on the outside by the skin and lined 
within by a sensitive membrane, called the conjunctiva. At the base 
of the lids the conjunctiva passes to the eyeball and forms a firmly 
attached covering over its front surface. It prevents the passage of 
foreign materials back of the eyeball and by its sensitiveness stimu- 
lates effort for the removal of irritating substances from beneath the 
lids. 

The Eyeball, or globe of the eye, is a contrivance for properly 
directing and focusing light waves upon a sensitized nervous surface 
which it incloses and protects. In shape it is nearly spherical, being 
about an inch in diameter from right to left and nine-tenths of an 
inch both in its vertical diameter and from front to back. It has 
the appearance of being formed by the union of two spherical seg- 
ments of different sizes. The smaller segment which forms about 
one-sixth of the whole, is set upon the larger and forms the projecting 
transparent portion in front. The walls of the eyeballs are made up 






EL EM EX IS OF PHYSIOLOGY. 



of three separate layers or coats — an outer, a middle, and an inner 
- — while the interior consists of liquid and solid portions. 
The Outer Coat surrounds the entire globe of the eye and 
consists oi two parts — the sclerotic coat and the cornea. The scle- 
rotic coat covers the 
greater portion of the 
larger spherical segment 
and is recognized in front 
as the "white of the eye." 
It is composed mainly of 
fibrous connective tissue 
and is dense, opaque, and 
tough. It preserves the 
form of the eyeball and 
protects the portions 
within. It is pierced at 
the back by a small open- 
ing which admits the op- 
tic nerve and in the front 
by a large opening which 
receives the cornea. The 
cornea forms the trans- 
parent covering over the 
lesser spherical segment 
of the eyeball and fits 
into a groove in the scle- 
rotic coat like a watch- 
glass into its case. It 
has a complex structure, consisting in the main of a transparent form 
of connective tissue, and serves the purpose of admitting light into 
the eyeball. 

The Middle Coat consists of three connected portions — the 
choroid coat, the ciliary process, and the iris — which together sur- 
round the larger spherical segment. They are all highly vascular 
and contain the blood supply for the greater portion of the eyeball. 
The choroid coat lies immediately beneath the sclerotic coat at 
all places except a small margin toward the front of the eye. It is 
composed chiefly of blood vessels and a delicate form of connective 
tissue that holds them together. It contains numerous pigment cells 




Fig-. 40. Diagram of the eyeball in position. 1. Yellow 
spot. 2. Blind spot. 3. Retina 4. Choroid coat. 5. Scle- 
rotic coat. 6. Crystalline lens. 7. Suspensory ligament. 8- 
Ciliary processes and ciliary muscle. 9. Iris containing the 
pupil. 10. Cornea. 11. Lymph duct. 12. Conjunctiva. 13. 
Inferior and superior recti muscles. 14. Optic nerve. 15. 
Elevator of the eyelid. 16. Bone. A. Posterior chamber. 
B. Anterior chamber. 



THE EYE. 161 

(Fig. 2) which give the choroid a dark appearance and serve to absorb 
surplus light. Near the junction of the sclerotic coat and the cornea, 
the choroid separates from the outer wall and forms, by a number of 
folds, a slight projection into the interior space. These are called the 
ciliary processes. The effect of the folds is to collect a large number 
of capillaries into a small space and to give this part of the eyeball 
an extra supply of blood. Between the ciliary processes and the scle- 
rotic coat is a small muscle containing both circular and longitudinal 
fibers, called the ciliary muscle. 

The iris is a continuation of the choroid coat across the front of 
the eyeball. It forms a dividing curtain between the two spherical 
segments and is the part which gives the color to the eye. At its 
center is a circular opening called the pupil which admits light into 
the back part of the eyeball. By means of two sets of muscle fibers 
in the iris, it is able, by varying the size of the pupil, to regulate the 
quantity of light that enters. One set forms a thin muscular band 
w T hich encircles the pupil and serves as a sphincter to close the opening. 
Opposing this are radiating fibers which pass from the pupil to the 
outer margin of the iris. Both muscles act reflexively and are stim- 
ulated by variations in the light falling upon the retina. 

The Inner Coat, or Retina, is a delicate membrane contain- 
ing the expanded portion of the optic nerve. It rests upon the choroid 
coat and spreads over about two-thirds of the posterior surface of the 
eyeball. Although not more than one-fiftieth of an inch in thickness, 
it presents a very complex structure, essentially nervous, and is made 
up of several distinct layers. Of chief importance is the layer of 
cells which are acted upon directly by the light and are named from 
their shape, the rods and cones. In contact with these, but occupy- 
ing a separate layer, are the ends of small afferent nerve cells which 
communicate at the opposite ends with another layer of nerve cells 
from which fibers pass to form the optic nerve. 

In the center of the retina is a slight depression which has a 
faint yellowish color and is called the yellow spot. This is the part 
of the retina most sensitive to light. Directly over the point of 
entrance of the optic nerve is a small area from which the rods and 
cones are absent and which, therefore, is not sensitive to light. This 
is called the blind spot. 

Experiments. 1. Place a clear but rather concentrated solution of 
chrome alum in a glass vessel with flat sides and hold it between the eye and 
11 



162 ELEMENTS OF PHYSIOLOGY. 

the light from a window. If the eye be closed for a short time before looking 
at the solution,, a round, rose-colored spot will be temporarily seen. This effect 
is due to the absorption by the yellow spot of certain light rays that pass 
through the solution. 

2. The presence of the blind spot may be proven as follows: Close the left 
eye and with the right gaze steadily at the spot on the left side of this page. 
Then starting with the book a foot or more from the face, move it slowly 



toward the eye. A place will be found where the spot on the right entirely 
disappears. On bringing it nearer, however, it is again seen. As the book 
is moved forward or backward, the position of the image of this spot on the 
retina changes. When the spot can not be seen, its image falls on the blind 
spot. 

The Crystalline Lens. Immediately behind the iris and 
touching its posterior surface is a transparent, rounded body, called 
the crystalline lens. It is about one-fourth of an inch thick and one- 
third of an inch through its long diameter and is more curved on its 
posterior than on its anterior surface. It is inclosed in a membranous 
capsule, the edges of which connect with an extension of the choroid 
coat, called the suspensory ligament. Both the lens and the capsule 
are highly elastic. 

The lens, together with the suspensory ligament and the ciliary 
processes, form a partition across the eyeball. This divides the eye 
space into two separate compartments which are filled with the so- 
called humors of the eye. The front cavity of the eyeball, which is 
subdivided into an anterior and a posterior chamber by the iris, is 
filled with the aqueous humor. This is a clear, watery, lymph-like 
liquid which contains an occasional white corpuscle. It has a feeble 
motion and is slowly but continuously added to and withdrawn from 
the- eye. It is supplied mainly by the blood vessels of the ciliary 
processes and finds a place of exit through a small lymph duct at the 
edge of the cornea. (Fig. 40.) 

The back part of the eyeball is filled with a soft jelly-like sub- 
stance, called the vitreous humor. It is in contact with the surface 



THE EYE. 163 

of the retina and the attachments of the lens, being separated only by 
a thin covering of its own, called the hyaloid membrane. 

Both the aqueous and vitreous humors act as refractive media 
and aid in keeping the eyeball in shape. 

Dissection of the Eyeball. Procure from the butcher two or more eyeballs 
obtained from cattle. After separating the fat, connective tissue, and muscles, 
place in a shallow vessel and cover with water. Insert a blade of a pair of sharp 
scissors at the junction of the cornea with the sclerotic coat and cut from this 
point nearly around the entire circumference of the eyeball, passing near the optic 
nerve. Spread open the parts in the water and identify the different structures 
from the descrij)tions in the text. 

Open the second eyeball by simply removing the cornea and examine the 
parts in front of the lens. 

How We See. To see an object four things must happen: 1. 
Light waves from the object must enter the eyeball. 2. These through 
the formation of an image are made to stimulate a portion of the 
retina which corresponds in form to that of the object. 3. Nervous 
impulses, started at the retina, pass to the visual area of the cerebrum. 
4. This becoming active, gives rise to the sensation of sight. 

Focusing Power of the Eyeball. From the cornea in front 
to the surface of the retina at the back of the eyeball, is a continuous 
series of transparent, refractive media. Name them. At two places, 
bodies corresponding to lenses are found. One of these is the cornea 
with its inclosed fluid ; the other is the crystalline lens. These lenses 
cause light waves from objects to form images on the retina, for the 
same reason that the glass lens forms the image of the candle on the 
screen. Fig. 39. The iris, in addition to regulating the quantity of 
light, also causes it to fall in the center of the crystalline lens, the part 
that focuses most accurately. With the exception of the cornea the 
eyeball closely resembles a photographer's camera and is comparable 
to it, part for part. Its general structure and action may be imitated 
in the following manner : 

In the center of one end of a crayon box, having a tight fitting lid, cut a hole 
half an inch in diameter. Fasten over this a small tin plate which has in 
its center a smooth, round hole less than one-fourth of an inch in diameter. 
Back of the hole fasten by a suitable support a convex lens. At the upper left 
hand corner of the box, cut another opening, one-fourth of an inch in diameter. 
Now fit a stiff piece of white paper in the back end of the box, so arranged that 
its position may be shifted. 



164 ELEMENTS OF PHYSIOLOGY. 

If the lid be placed on the box and the opening in the center turned toward 
a window, an inverted image will be seen on the screen by looking in the hole 
at the corner of the box. Care must be taken that the head does not obstruct 
the light which passes from the window to the hole. 

Because of the difference in density between air and the aqueous 
humor, the greatest degree of refraction occurs at the surface of the 
cornea. 

Accommodation. A difficulty in focusing arises from the fact 
that the angle of divergence of light waves entering the eye from ob- 
jects varies with their distance. Since the waves from any given point 
on an object pass in straight lines in all directions, waves entering the 
eye from distant objects are more nearly parallel than those from near 
objects. To adjust the eye to different distances, requires some 
change in the refracting parts that correspond to the degree of diverg- 
ence of the light. This is accomplished by the crystalline lens 
through changes in its curvature, 

When the divergence increases, as it does on looking from distant 
to near objects, the lens becomes more convex. When the divergence 
of the light diminishes, as in changing to distant vision, the lens be- 
comes flatter and thinner. This changing of the lens to focus light 
from different distances, is called accommodation. 

The method employed to change the shape of the lens is difficult 
to determine and different theories have been advanced. The follow- 
ing, proposed by Helmholtz, is the one most generally accepted : 

The lens is suspended back of the pupil by its membranous cap- 
sule and the suspensory ligament. The suspensory ligament is at- 
tached to the sides of the eyeball in such a manner that it exerts con- 
tinuous tension on the membranous capsule which, in its turn, exerts 
pressure on the sides of the lens, tending to flatten it. 

This arrangement brings the elastic force of the eyeball into 
opposition with the elastic force of the lens. The ciliary muscle plays 
between the two in the following manner : 

To thicken the lens, the ciliary muscle contracts, pulling forward 
the suspensory ligament and releasing its tension on the membranous 
capsule. This permits the lens to thicken by virtue of its own elastic 
force. To flatten the lens the ciliary muscle relaxes, the elastic force 
of the eyeball resumes the tension on the suspensory ligament and 
the membranous capsule resumes its pressure against the sides of the 
lens. This pressure, acting against the elastic force of the lens, flat- 
tens it. 



THE EYE. 



165 




In other -words, when the ciliary muscle is relaxed, the lens is in 
the condition of a rubber ball with a weight upon it. By contracting, 
the muscle removes this pressure and permits it to assume its natural 
shape which is one of greater convexity than the one in which it is 
held. 

Movements of the Eyeball as a whole are brought about by 
the action of six small muscles. Four of these, named from their posi- 
tions the superior, inferior, internal, 
and external recti muscles, are at- 
tached at one end to the sides of the 
eyeball and at the other to the back of 
the orbit. These in the order named 
are able to turn the eyes upward, 
downward, inward, and outward. 
The other two, the superior and in- 
ferior oblique muscles, supplement cer- 
tain movements of the recti muscles 
and, in addition, serve to rotate the 
eye. The movements of the eyeball 
are similar to those of a ball and 
socket joint. (Fig. 41.) 

Visual Sensations include sensations of color and what is called a general 
sensibility to light. Proof of the existence of these types of sensation is found 
in color blindness, a defect which renders the individual unable to distinguish 
color when he is still able to distinguish objects. Color sensations are the re- 
sults of light waves of different lengths acting on the retina. While the method 
by which waves of one length produce one kind of sensation and those of another 
length a different sensation, is not understood, it seems quite possible that the 
cones are the portions of the retina acted upon to produce the color. On the 
other hand the rods are sensitive to all wave lengths and give rise to general 
light sensations. Many of the sight impressions are not sensations at all, but are 
to be classed as 

Visual Inferences. "Seeing" is very largely the mental interpretation of 
the primary sensations described above and the conditions under which they 
occur. For example, our ability to see objects in their natural position when 
their images are inverted on the retina is explained by the fact that we are not 
conscious of the retinal image but of the mind's interpretation of it through ex- 
perience. 

Experience has also taught us to locate objects in the direction toward which 
it is necessary to turn the eyes in order to see them. In other words we see 
objects in the direction from which the light enters the eyes. That the object is 
not always in that direction is shown by the image in a mirror. The size and 



Fig. 41. Muscles of the right eyeball. 
1, 2, 3, 4. The inferior, superior, external, 
and internal recti muscles. 5, 6. Inferior 
and superior oblique muscles. 



166 ELEMENTS OF PHYSIOLOGY. 

form of objects are inferences based largely upon the size and form of the area 
of the retina which is stimulated. We judge of distance by the effort required 
to converge both eyes on the same object, by the amount of divergence of the 
waves entering the pupil, and also by the apparent size of the object. 

Binocular Vision. In addition to directing the eyeballs so that light waves 
from any given object may enter them to the best advantage the muscles also 
enable the two eyes to be used as one. When the eyes are directed toward an 
object an image is formed on the retina of each and double vision is prevented 
only by the images falling on corresponding retinal areas. In each act of seeing, 
it becomes the task of the superior and inferior recti muscles to keep the eyes 
in the same plane and that of the internal and external recti muscles to produce 
the requisite amount of convergence. If slight pressure is exerted against one 
of the eyes this action of the muscles is prevented and objects are seen double. 
The advantages of two eyes over one in seeing, lie in the greater distinctness 
and broader range of vision and in the greater correctness of judgments of 
distance. 

The Lachrymal Apparatus. Some of the methods of pro- 
tecting the eyeball were indicated in the description of the cavity in 
which it is placed. It is further protected by the continual wetting 
of its front surface by a liquid secreted for this purpose, called tears. 

The lachrymal glands are situated at 

the upper and outer margins of the orbits. 

•^Jl^ i They have the general structure of salivary 

z^^T"^ s\ glands and discharge their liquids by small 

/~ — -^ti ,■ i ducts beneath the upper lids. From here 

the tears spread over the surface of the eye- 
balls and find their way in each eye to two 
small canals whose openings may be seen 
on the edges of the lids near the inner cor- 
ner. These canals unite to form the nasal 
mSs g tuteto5hlSoS r oltEJ ly eyl duct which conveys the tears to the nasal 
*& of eVetri! g Ki lua °" cavity on the same side of the nose. Fig. 

42. When by evaporation the eyeball 
becomes too dry, the lids close reflexively and spread a fresh layer of 
liquid over the surface. 

Visual Defects. The delicacy and complexity of the sense organs of sight, 
render them liable to a variety of defects. An eye in a normal condition is able, 
when relaxed, to focus light from objects which are twenty feet or more away 
and is able to accommodate itself to objects as near as five inches. An eye is 
said to be myopic or short-sighted when it is unable to focus light waves from 
distant objects. In such an eye the ball is too long for the converging power 
of the lenses and the image falls in front of the retina. A long-sighted or hyper- 



THE EYE. 167 

metropic eye is one which can focus waves from distant objects but not those 
from near objects. In such an eye the ball is too short for its converging power 
and the image of the object if formed would fall behind the retina. These de- 
fects in focusing are remedied by wearing spectacles whose lenses are shaped so 
as to counteract them. Short-sightedness is corrected by means of a concave 
lens and long-sightedness by a convex lens. 

In astigmatism the parts of the eye fail to form an image in the same plane. 
As a result one part of the object will be seen distinctly while the other is 
dim or blurred. The cause lies in some defect in the curvature either of the 
cornea or crystalline lens. It is remedied by lenses ground to correct the partic- 
ular defects which are present in a given eye. 

Whenever defects in focusing are present, particularly in astigmatism, extra 
work is thrown on the muscles which move the eyeballs. The result is fre- 
quently to produce a condition known as "muscle weakness" which renders it both 
difficult and painful to use the eyes. Even after the defect in focusing has 
been remedied, the muscles recover slowly and must be used with great care. 

Oare of the Eyes. If proper care is exercised in the use of 
the eyes many of the common ailments and defects may he avoided. 
Anyone, whether his eyes are weak or strong, will do well to observe 
the following precautions : 

1. Never read when the light is very intense or very dim. 2. 
When the eyes hurt quit using them. 3. Never hold a book so that 
the smooth page reflects light into the eyes. The best way is to sit or 
stand so that the light passes over the shoulder to the book. 4. Never 
study by a lamp that is not shaded. 

If the eyes are weak use them less and wash them frequently in 
warm water or water containing enough salt to smart them slightly. 
When anything serious affects the eyes consult either an oculist, or a 
physician who has made a special study of the eye. 

Students in the laboratory frequently, through accident, get 
strong chemicals, as acids and bases, in the eyes. The first thing to 
do in such cases is to flood the eyes with water. Any of the chemical 
remaining may then be counteracted with the proper reagent, care 
being taken to use a very dilute solution. For an acid use sodium 
bicarbonate (cooking soda) and for a base use a dilute solution of 
acetic acid (vinegar). To guard against getting the counteractive 
agent too strong for the inflamed eye, it may first be tried on an eye 
that has not been injured. 

The eyes of school children often have defects, unknown to them- 
selves or their parents, which render close work burdensome and cause 
pain in the eyes, headache, and general nervousness. The precaution 



ELI HYSIOL: 

adopted by many school- I :. mining the eyes of all the efaUdbroi 
with a view to detecting defects and causing them tc 
most excellent and worthy of imitation. 

Summary. Sigfol _- w si important of the sensation- - 
complished through the action of light vares npon a sensitized nerv - 
surface called the retina. By means of refractiYe agents, forming 
part of the eyeball in front of the retina, the light from ol ; Is - 
focused npon it. stimulating in this "way an area corresponding in form 
" the object. The greatest degree of refraction occurs at the aran, 
while the crystalline lens serves as the instrument of aceommiodatioiiL 
To adapt the eyeballs to their work, they are controlled 
kept constantly moist ; and are protected by a variety of ager ; . - - 

Review Questions. 1 . "Cnder what conditions axe light wares ret e 
transmitted, and absorbed? 

2. What is the origin of the light waTes which enable us to see obje - 

3. How mar the light reflected from an object form an image of lha: 

4. What different things must happen in order to see an object ? 

5. What portions of the eyeball transmit light? What absorb lig: .: W: " 
reflect light? What refract light? 

6. Show how the iris, the crystalline lens, the retina, the cilia:; 
and the cornea aid in seeing. 

Trace a ray of light from a -visible object through the different med: 
the retina. 

E What change in the shape of the crystalline lens occurs, when we look 
from a distant to a near objeet ? Why is this change necessary? How is ft 
brought about ? 

9. Show how the proper lenses remedy short- and long-sightedness. 

10. Of what importance are the muscles attached to the outside of the 
eyeballs ? 

11. Describe the conjunctiva and give its functions. Why should it be 
sensitive ? 



CHAPTER XXI. 

THE GENERAL PROBLEM OF KEEPING WELL. 

The special hygiene of the different organs of the body having 
been considered in connection with their study, it still remains to ob- 
tain a general view of the problem of keeping well. Health may be 
described as that condition of the body during which each organ does 
the work devolving upon it and, at the same time, is adjusted in its 
activity to the other parts of the body. Weakness of any organ which 
impairs its function or interferes with its adjustment to other parts is 
known as disease. The problem of keeping well consists in part in the 
detection and removal of the external causes of disease and in part in 
the building up and strengthening of such organs or parts of the body 
as may be weak. 

Causes of Disease. Disease has its origin in conditions which, 
by their effect upon the body, weaken one or more of its parts or inter- 
fere with its normal method of operation. Some of these conditions 
are remote and, as those concerned in inherited defects, are beyond the 
control of the individual. Others are the results of negligence in the 
observance of well recognized hygienic laws. Others still are of the 
nature of influences which, like climate, the house in which one lives, 
or one's method of gaining a livelihood, produce changes in the body, 
imperceptible at the time, but which, in the long run, profoundly 
affect the health. And last, but not least, may be mentioned the effect 
of micro-organisms or germs which are known by the general name 
of bacteria. 

Effects of Bacteria. While there are many forms of bacteria 
that have no ill effect upon the body and others that are thought to aid 
it in its work, there are many well known varieties which produce 
effects that are decidedly harmful. They find an entrance into the 
system through the lungs, the digestive tract, or the skin and, living 
upon the liquids and tissues, multiply with great rapidity until they 
permeate the entire body. They not only destroy the protoplasm of 
12 169 



170 ELEMENTS OF PHYSIOLOGY. 

the various tissues, but deposit waste products, called ptomaines, which 
act as poisons. Infectious diseases as measles, smallpox, scarlet fever, 
tuberculosis, la grippe, and diphtheria are due to specific forms of 
bacteria which are able to pass from those having the disease to those 
who are well — a fact which accounts for their contagious nature. Other 
diseases as typhoid, yellow and malarial fevers, cholera, and blood 
poisoning are due also to specific forms of bacteria. In addition to 
these it is quite probable that many forms of bacteria exist whose 
effects are not so marked, but which interfere with the normal condi- 
tion of the body.* 

Prevention of Bacterial Diseases. In preventing the spread 
of infectious disease the problem belongs as much to the community as 
to the individual. In fact the spreading of such diseases as smallpox 
and yellow fever, can only be checked by the co-operation of the com- 
munity under the direction of the strong arm of the law. Isolation of 
individual patients and of infected neighborhoods is absolutely neces- 
sary and, while this may inflict hardship on the few, it is the only safe- 
guard for the many. Great care must be exercised that nothing used* 
in connection with the sick shall serve as a retainer or carrier of germs. 
All clothing, bedding, or furniture should be thoroughly disinfected or 
burned. All discharges from the body of the sick should be treated 
with disinfectants and buried deeply at a remote distance from any 
water supply to the house. Buildings in which the sick have been cared 
for should be thoroughly disinfected and cleaned before they are again 
occupied. The walls of the rooms should be repapered or calcimined 
and the woodwork repainted, while the out buildings should also be 
disinfected and cleaned — the object being to completely destroy any 
germs which, if left, might cause a fresh breaking out of the disease. 

In combating bacteria of less virulent types, the attention should 
usually be directed to conditions in the home or immediate neighbor- 
hood that are responsible for their development or transportation. Con- 
ditions for their development are fully supplied by places containing 
decaying vegetable or animal products, moisture, and a moderate 
degree of warmth. Marshes, cesspools, damp cellars, poorly lighted 
and ventilated rooms, and all places of filth produce bacteria of many 



*The arctic explorer Nansen states that during all the time that his party was 
exposed to the severe chill of the arctic region, no one was attacked by a cold, 
but on returning to a warmer climate they were subject to colds as usual. The 
difference he attributes to the absence of bacteria in the severe arctic climate. 



THE GENERAL PROBLEM OF KEEPING WELL. 171 

kinds in abundance. The water which one uses may, if it contains a 
small per cent of organic impurities, support such dangerous bac- 
teria as those of typhoid fever. This water becomes especially dan- 
gerous when the supply is low and the impurities are concentrated. 
Fruits and vegetables, because of the localities of their growth or 
method of storage, may also contain dangerous bacteria. Impure water 
should be thoroughly boiled and all food suspected of being contami- 
nated, should be thoroughly cooked before using. The common dust 
everywhere so prevalent during the summer and so abundant indoors 
in the winter, is an important factor in the spreading of bacteria. Air 
containing dust should be breathed as little as possible and only through 
the nostrils. When one is compelled, as in the sweeping of halls or 
rooms, to breathe dust-laden air for some time, he should inhale 
through a moistened sponge or cloth secured in front of the nostrils. 
Domestic pets as well as household pests — rats and mice and various 
insects — are also responsible for the spreading of certain forms of 
bacteria. * 

Sanitary Condition of the Home. Much of the danger 
from bacteria may be prevented by instituting and maintaining proper 
sanitary conditions in and about the home. The home, being the 
feeding and resting place of the entire family, and the place where 
every one spends a large part of his time, is the most important factor 
in one's physical, as well as moral, environment. For this reason 
there is no place where careful attention to hygienic requirements will 
yield better results. 

One of the first requisites of the home is a suitable location for 
the house. The house should be built upon ground that is well drained 



* It has recently been proven beyond question that the common mosquito 
is largely responsible for the spreading of the malarial plasmodium. By sucking 
the blood of those suffering from malaria, and perhaps by other means not under- 
stood, he becomes infected with organisms which he injects beneath the skin of his 
victims who may be well. It is therefore a safe precaution to limit as much as 
possible the production of mosquitoes in any neighborhood. All small bodies of 
standing water should be drained or, where this is' not possible, covered with a 
thin layer of kerosene. 

The common house-fly is also an important agent in the spreading of bac- 
teria. Feeding as it does on filth of all kinds, it is easy for it to transfer the 
bacteria that may stick to its body, to the food which is supplied to the table. 
Screens should be employed for keeping flies out of the house and material in 
which they develop, such as the refuse from stables, should not be allowed to 
accumulate. 



172 ELEMENTS OF PHYSIOLOGY. 

and, if natural drainage is lacking, artificial drainage should be sup- 
plied. Xo marsh or swamp should be within a quarter of a mile of 
the house and, if so near, should be in the direction toward which 
the wind usually blows. A stone foundation should be provided and 
there should be left at least eighteen inches of ventilated air space 
between the ground and the floor. Ample provision should be made 
for pure air and sunlight in all the rooms. The cellar, if one is 
desired, should be constructed with special care. It should be per- 
fectly dry and provided with windows for both light and ventilation. 
Adequate means should be provided, by sewage pipes and other means, 
for the disposal of all waste from the kitchen. Where drainage pipes 
are provided, care must be taken to prevent the entrance of sewer gas 
into the house and also the passage of material from these pipes into 
the water supply. The placing and connecting of sewer pipes should 
always be under the direction of an expert mechanic. 

But it matters not how carefully a house has been constructed 
from a sanitary standpoint, it requires the constant care of an intelli- 
gent housekeeper to keep it a healthful place in which to live. Daily 
cleaning and airing of all living rooms is necessary while such places 
as the kitchen, the cellar, and closets need extra thoughtfulness and, 
at times, hard work. Moreover the problem is not all indoors. The 
immediate premises must be kept clean and sightly. All decaying 
animal and vegetable matter should be removed. Rubbish of any 
kind must not be allowed to accumulate and disinfectants should be 
used freely. It is thus seen that home sanitation consists not of one, 
but of many problems, all more or less complex and none of which can 
be slighted or turned over to the novice. Not the least of such prob- 
lems is that of providing an adequate and healthful 

Water Supply. Water very readily takes up and holds the im- 
purities with which it comes in contact and for this reason should 
either be exposed as little as possible in the process of collecting or 
separated from its impurities afterward. Where cistern water is used 
care must be taken to prevent filth from the roof, waterpipes or soil 
from getting into the reservoir. Where no means of filtering is pro- 
vided, water should be collected from the roof only after it has rained 
long enough for the roof and pipes to have been cleaned, and water 
should be collected in the winter time rather than in summer. The 
cistern should have no leaks and the top should be inclosed to prevent 
the accidental falling of small animals or rubbish into the water. 



THE GENERAL PROBLEM OF KEEPING WELL. 173 

Shallow wells are to be condemned, as a rule, because of the likelihood 
of surface drainage and water from springs should, for the same rea- 
son, be used with caution. Deep wells, that are kept clean, usually 
may be relied on to furnish water free from organic impurities, but 
such water often holds in solution so much of mineral impurities as to 
render it unfit for drinking purposes. 

Relation of Vocation to the Health. With a few exceptions, 
the pursuit of one's vocation or calling in life does not supply either 
the quantity or kind of activity that is most in harmony with the plan 
of the body. Especially is this true of work that requires most of the 
time to be spent indoors and which exercises but a small portion of 
the body. The effect of such vocations, if not counteracted, is to 
weaken certain organs of the body, thereby disturbing the functional 
equilibrium of its parts — a result that may be brought about either by 
the overwork of particular organs or through lack of sufficient exercise 
of others, Herein lies the explanation of the observed fact that people 
of the same calling in life have similar diseases. If, as too often hap- 
pens, the vocation is pursued under conditions of strain, or during 
periods that are too prolonged, exhausting the entire body as well as 
the organs most directly concerned, the effect is to intensify the ten- 
dencies incident to the work and to induce additional forms of weak- 
ness. The avoidance of whatever tendencies to disease that may exist 
in one's calling in life, is necessary both because of their bearing upon 
one's ability to work and upon the ability of the body to resist attacks 
of bacteria. 

The Remedy lies in two directions — that of spending sufficient 
time away from one's work to allow the body to regain its normal con- 
dition and that of counteracting by special exercise or other means the. 
effect of the work. In most cases the first symptoms of weakness indi- 
cate a suitable remedy. Thus exhaustion from overwork suggests rest 
or recreation. The diverting of too much blood from other parts of 
the body to the brain suggests some form of exercise or work which 
will equalize the circulation. If feebleness on the part of the digest- 
ive organs is being induced, some natural method of increasing the 
blood supply to these organs is to be looked for, while effects arising 
from lack of fresh air and sunlight are counteracted by the spending 
of more time out of doors. 

In the counteraction of tendencies to disease and in the maintenance of 
the functional equilibrium of the body, no agent has yet been discovered of 



174 ELEMENTS OF PHYSIOLOGY. 

greater importance than physical exercise,, when applied systematically and per- 
sistently. This may consist of exercises which call into activity, with more or 
less uniformity, all the muscles of the body or that which may be concentrated 
upon special parts. Where general tonic effects are desired, the exercise should 
be well distributed, but where counteractive and remedial effects are wanted it 
must be applied chiefly to the parts that are weak or that have not been called 
into action by the regular work. Unfortunately health is sometimes confused 
with physical strength and the exercise directed mainly to the stronger parts of 
the body with the effect of making them still stronger. Xot only is health not to 
be measured by the pounds one can lift or some gymnastic feat one may be able 
to perform, but the possession of great muscular power may. if the heart and other 
organs be not proportionately strong, prove a menace to the health. This being 
true, one having his health primarily in view will use physical exercise in 
part, at least, as a means of diverting an increased blood supply to the parts that 
are weak. 

Since the body, like a chain, can be no stronger than its weakest part, this 
is clearly the logical method of fortifying it against disease. 

Value of Work. Since there may exist in the nature of one's 
vocation certain causes of disease, it must not be inferred that work, 
in itself, is detrimental to the health. Such an inference would be 
erroneous and not at all in keeping with the plan of the body. Health 
demands activity and those forms of activity that provide a systematic 
outlet for one's surplus energy and compel the formation of regular 
habits of eating, sleeping, and exercise best serve the purpose. Work 
furnishes activity of this kind and serves also as a safeguard against 
the unhealthful and immoral habits contracted so often from idleness. 
Even physical exercise, which has for its purpose the counteraction of 
tendencies to disease, may frequently be of the nature of useful work 
without at all diminishing its desired effects. 

The Mental- Attitude. While a proper thoughtfulness and care 
for the body is both desirable and necessary, it is also true that over- 
anxiety about, or an unnatural attention to, the needs of the body, is 
objectionable from a hygienic standpoint. Observance of the laws of 
health, therefore, should be natural and, without special effort, as a 
matter of habit. The attention should never be turned with anxiety 
upon any organ or process, but the mental attitude should at all times 
be that of confidence in the power of the physical organization to do its 
work without aid or interference. Fear, which is a disturbing and 
paralyzing factor in the animal economy, must if possible be sup- 
planted by courage and hopefulness. 

Nor does living hygienically preclude the idea of strenuous effort. 
The plan of the body is such as to withstand great strain and hard 



THE GENERAL PROBLEM OF KEEPING WELL. 175 

usage, if they be not too prolonged, in fact, to meet any and all ordi- 
nary demands that may be made upon it. Hygiene means nothing more 
than the application of the same intelligence and practical common- 
sense to the care of the body that the skilled mechanic would apply 
to an efficient but intricate and valuable piece of machinery. And, 
just as in the case of the machine, care of the body keeps its efficiency 
at the maximum and lengthens the period that it may be used. This 
end and aim of hygienic living are best attained by cultivating that atti- 
tude of mind toward the body which avoids interference in the vital 
processes and which permits the natural appetites, sensations, and de- 
sires to indicate very largely the needs of the body. 

Summary. The solution of the problem of keeping well is, for 
each individual, the living of that life which is in closest harmony 
with the plan of the body. Such a life, because of differences in 
physical organization, as w T ell as differences in environment and occu- 
pation, cannot be the same for all persons. All, however, must ob- 
serve the conditions under which the body may be used without injur- 
ing it and the special hygienic laws relative to the care of particular 
organs. Causes of disease, whether they be found in one's environ- 
ment, vocation, or method of recreation must be avoided or counter- 
acted. 

While the problem is beset with such difficulties as lack of suffi- 
cient knowledge, inherited weakness, and time and opportunity for 
doing what is known to be best for the body, yet study and work that 
has for its aim the preservation or improvement of the health is always 
worth while. Health is its own reward. 

Practical Questions. 1. State the important differences between a con- 
dition of health and one of disease ? 

2. In what general ways may disease originate in the body? 

3. What conditions in the life of a student may, if uncounteracted, lead to 
poor health? 

4. In what different ways may one's physical environment affect his health? 

5. Describe a model sanitary home. 

6. Of what special advantage are the parks and pleasure grounds in a 
city to the health of its inhabitants? 

7. Describe the necessary precautions for preventing the spread of infectious 
diseases. 

8. How are the bad effects of indoor life to be counteracted? 

9. Describe the general methods of preventing the entrance of bacteria into 
the body. 

10. Discuss the hygienic value of work. 



SUMMARY OF PART II. 

Th- or cell group must have its parts controlled and co- 

ordinated. It must be moved from place to place. It must be con- 
stantly adjusted in its various activities to the physical conditions sur- 
rounding it. To accomplish these purposes there is employed: 

1. The skeleton which supplies a framework, the parts of which 
are movable upon each other, making of the body a machine capable of 
motion. 

2. The muscular system which supplies the necessary force for 
moving the machine. 

3. The nervous system which (a) controls and co-ordinates the 
various activities and (b) provides for the intelligent management of 
the body. 

Eeview plan of the lx page r . and _riieral summary, page 
salt figure 1.) 



176 



APPENDIX. 



To Prepare Oxygen. Mix thoroughly a heaping teaspoonful of potassium 
chlorate with half as much manganese dioxide and place in a test tube six inches 
long. The top of the tube should be tightly closed with a cork, through which 
passes the end of a small glass tube 15 inches in length. To secure the proper 
shape for passing the gas into receivers, this tube should be bent nearly at right 
angles about an inch above the cork and again slightly, about one-half an inch 
from the other end. 

For collecting the gas a wash basin and several large-mouthed bottles are 
required. Fill each bottle even full of water, place a stiff piece of paper over the 
mouth, and invert, without spilling, in the pan, which should contain water to the 
depth of three-fourths of an inch. 

When everything is ready heat the test tube over the flame of an alcohol 
lamp, bringing it near enough for the flame to spread over the end of the tube. 
When the gas begins to pass off insert the end of the tube under one of the bottles. 
Leave the bottles of gas inverted in the pan until ready to use the gas. On remov- 
ing keep the bottles tightly covered. 

To Destroy the Brain of a Frog. For certain experiments in which 
live frogs are used the most successful as well as the most humane way of manag- 
ing them is to destroy the brain. This puts the frog under the complete control 
of the operator and at the same time destroys all sensation. 

Make an incision with a sharp knife, over the spinal cord where the head 
joins the body. Insert the blunted end of a wire, or a large knitting needle, and 
push it into the cavity occupied by the brain. Probe with the wire in different 
directions until sure that the different ganglia have been disorganized. When the 
frog drops into a relaxed and lifeless condition the operation is complete. 

To Collect Blood. If only a drop or two is needed it can easily be obtained 
from the finger. Wrap one of the fingers of the left hand with a handkerchief, 
from the hand down to the last joint. Bend this joint, give it a sharp, quick blow 
with the point of a clean pin or needle above the root of the nail. Pressure 
applied to the under side of the finger will force plenty of blood out through a 
very small opening. (To prevent any possibility of blood poisoning, the pin and 
finger may be washed with alcohol before making the incision.) 

If blood is needed in large quantities it must be obtained from the slaughter 
house. To be sure of securing the specimens of blood needed for the experiments 

177 



1 . 8 APPENDIX 

in Chapter II. take to the butcher three suitable vessels, upon which are pasted 
labels like the following: 



Fill % fall. While the j Fill 2 3 fall and set a- : Fill 2 ~ full and thor- 
: blood is cooling, stir rap- : side without shaking or : oughly mix with the liq- 

idly with the hand or a ■ stirring. : uid in the bottle. 

\ bunch of switches to re- ' 
: move clot. : 



Label Xo. 3 must be pasted on a bottle, having a tight fitting cork, which 
is filled one-fifth full of a saturated solution of Epsom salts. 

Lime-Water is prepared by dissolving lime in water. Fill a quart jar 
nearly full of water and add a few small lumps of fresh lime. Mix the two and 
let stand till all the undissolved lime settles to the bottom. This will require a 
day or more. Pour off and use the clear liquid above the lime. For additional 
supplies, refill the bottle with water. | Only fresh lime can be used in the prep- 
aration of lime-water.) 

Dissections are occasionally necessary in the study of physiology in order 
to obtain definite ideas of the structure and form of organs and tissues. In 
conducting a dissection care must be taken not to offend the sensibilities of 
pupils and not to cultivate a disregard for the lives of the lower animals. The 
skill of the operator and spirit in which the dissection is made have everything 
to do with the mental attitude of the pupils. A difficult dissection like that 
of the abdomen should not be undertaken before a class without previous ex- 
perience on the part of the teacher. Care must always be exercised in the matter 
of cleanliness and the escape of blood should be prevented as far as possible. 
The necessity for gaining accurate information at first hand, which is the 
excuse for the dissection, must be kept prominently in mind. 

Equipment. Nearly all of the apparatus and materials called for in this 
book may be found in the physical, chemical, and biological laboratories of the 
average high school. There should be ready, however, for frequent and con- 
venient use. the following: One or more compound microscopes with two-thirds 
and one-fifth inch objectives ; a set of prepared and mounted slides of the various 
- of the body: a set of dissecting instruments, including bone forceps; a 
mounted human skeleton and a manikin or a set of physiological charts ; a set 
of simple chemical apparatus including bottles, flasks, test tubes, and evaporat- 
ing dishes; and a Bunsen burner or some other means of supplying heat. 

The few chemicals required may be obtained from a drug store or from the 
chemical laboratory. Access to a work bench having a set of carpenter's tools 
will enable one to prepare many simple pieces of apparatus as they are needed. 

Physiological Charts are easily prepared by teachers or pupils by care- 
fully enlarging the more important illustrations found in text-books or by work- 



APPENDIX. 179 

ing out original sketches and diagrams. These, if drawn on heavy Manilla paper, 
may be hung on the wall as needed and preserved indefinitely. By the use of 
colors, necessary contrasts are drawn and emphasis placed on parts as desired. 
The author has for a number of years used such home-made charts in his teaching 
and has found them quite satisfactory. His plan has been to first draw on heavy 
Manilla paper, cut in sizes of two by three feet, the general outline in pencil 
and then to mark over this with the desired colors. There is of course an oppor- 
tunity for producing results that are artistic as well as practical and if one has 
time and artistic skill, better results can be obtained. Most of the cuts of this 
book are excellently suited to enlargment and, if properly executed, will provide 
a good set for general class purposes. 

A more expensive, but better method in the end, is that of making the 
drawings upon white window shades with water proof ink or with colored crayons. 
The rollers, if left attached, may be secured permanently to the wall and the 
drawings pulled down as they are needed. 

If the crayon colors show a tendency to rub off they may be "fixed" by 
spraying the drawing with a solution of shellac in alcohol. Artist's crayons, 
however, may be obtained that adhere to the paper or cloth. 



INDEX. 



Page. 

Abdomen 53-56 

Abdominal cavity 54 

Abdominal organs 55 

Abdominal walls 55 

Absorption 70-73 

Accommodation 164 

Afferent impulses 141 

Afferent nerve cells 131 

Air 29 

Air passages 31 

Air spaces (terminal) . . . . 32 

Albumin 47 

Of blood 11 

Albuminoids 47 

Alcohol, effects of 

On the blood 13 

On the organs of circulation. 22 
On the organs of digestion . . 68 

On the liver 139 

On the nervous system 139 

On the regulation of temper- 
ature 116 

Alcohol not a food 51, 74 

Experiments to illustrate effects 

of 57 

Summary of effects 139 

Storage of 74 

Alimentary canal 58 

Alimentary muscles 67 

Anatomy, defined 1 

Animal heat 80 

Aorta 20 

Appendix 177 

Aqueous humor 162 

Arachnoid membrane 124 

Arteries, structure of 18 

Important arteries 20 

Articulations 100, 101 

Assimilation 75 

Astigmatism 167 

Atmosphere 29 

Attraction sphere 4 

Auditory canal 151 

Auricle 151 

Automatic action 133 

Axis cylinder 125 

Axone 125 

Bacteria 169 

Basilar membrane 153 

Bathing 117 

Bellows, principle of 35 

Bile 65 

Binocular vision 166 

Bladder 86 

Blind spot 162 



Page. 

Blood 8-14 

Amount of 12 

Changes in 12 

Composition of 9 

Experiments with 8 

Properties of 8 

To collect 177 

Bone 93 

Composition of 93 

Properties of 93 

Structure of 94 

Bone cells 95 

Nourishment of 95 

Bones, table of 99 

Bowels, care of 68 

Canaliculi 105 

Capillaries 20 

Capsules, Malpighian -87 

Carbon dioxide 11, 42, 43, 85 

Carbohydrates 47 

Absorption of 71 

Digestion of 66 

Storage of 73 

Carpal bones 98 

Cells 3-5 

Activities of 5 

Kinds of 3 

Structure of 4 

Cell-body • 124 

Cell wall 4 

Central nervous system ..: 121 

Cerebellum ' 122 

Function of 132 

Cerebrum 119 

Functions of 135 

Cervical vertebrae 96 

Chemical affinity 78 

Chemical basis of the body 6 

Chemical changes in the body ... 40 

Chemical potential energy 78 

Chemical uniting 40, 45 

Charts, physiological 179 

Choroid coat 160 

Cigarettes 139 

Ciliary muscle 161 

Ciliary processes 161 

Ciliated epithelial cells 32 

Circulation of the blood 15-23 

Discovery of 15 

Necessity of 15 

Organs of 15 

Clothing 117 

Coagulation 11 

Cochlea 153 

Coffee 22 

Combustion 40, 45 

Compounds 39 



181 



a 



::■:>! i 



CondodLit ily of nenre 
Conjunctiva 

Co-ordination 

" ■ rnea 

Coronary circulation . 
Corpuscles 

7."rl 

White 

CTvstalline leu? 
Cuticle 

~~. :~ . :- -r_i 
Deglutition, steps in . . 
Dendrites 

- 

7 _- ---; Llirj :: : : :■-- 

r _t- _ : :r. . . .. . 

.' : _ z - : : 

Processes off 

7J :_t-: - ;"_.-., ni« 
7 : - - " -- 

Prevention off 

Of abdomen - 

Off evefeaM 

:-: :- - 

-- .---i.^- 

Off nerrou 

Z -: _ - - :: r : - - : 
Dnetless glands . - 



. a - . : . 

Elasticity off 

Eni " •;.. - 
ILzLi-rjTTiTi 

Kinetic 

Liberation off at 

; : :7- '•:■:- 
_ 7 :--::•,: 
-- : 7~ - - 
E - -".::•'. '---~'~ 



:_- 
:: 

9 

:: 

.. 123 

: : 
::: 

- 



r _ _ : 

... 64 
... 124 

:.::-:-:•: 

... 151 
...152 

151 

... 131 

... IS 
...142 



Eyeball 

_ _ - - : " - : 



' 

107 

79 

m 

71 

:i4 

ITU 
151 
159 

: - 



62 
124 

::; 

34 



65 



: " 

17© 

ITS 

53 

: : 

15 



_ 



Exercise, effetes of, 
On health .. 

:- 



- 



-Ill, 173, 174 
_- 

Ill 

138 

.83-91 

Plan off 86 

Quantity of exeretorv produc~ b 

Accommodation 164 

Blind spot . 162 

_ :!:■:•?::::: :: .:~r 

Digestion -57. 61, 63 

Effects of alcohol 

Elastkitv of arterie- . 18 

Energy " ; : 

'Lener- . 109 

Light 158 

-Z~Zi:-,~'.-.-~ :: :t-7 :::• v. ::i , : " 



Properties of carbon dioxide -1 

Purpose off respiration. . 1 

_ :-::-- : :-:: ' :-:7r; '■' 

Ee€ex action 130 

Sound -- - -^ 

Structure off eyeball 164 

Temperature sensations 144 

Touch 143 

Working off heart 17 

Yelloir spot 162 

J .- : :-" -77:1 :z :: 

Digestion off . 66 

Storage off . . . 

Femur ... 

Fibrin ... 

j :'-?:- :^i - 11 

Focusing of eyeball 163 

Composition off 47 

77 ".-;.".-• :' 

Xitrogenous 46 

Non-nitrogenous Mi 

Purposes off . .45 

Substances suitable for 

Tables of .46. 50 

F:..i -:mt> ........ « 

Food supply to the table 49 

Focusing of eyeball . 163 

Fore-brain 119 

Fractures of bone . . 102 

Fretting and worrying 177 

Gall bladder ........ .65 

Ganglia, structure off 126 

Dorsal root . 123 

Sympathetic 123 



INDEX, 



183 



Page. 

Gastric juice 63 

Gastric glands 63 

Glands 83 

Kinds of 83 

Structure of 83 

Globulin 11 

Glottis 148 

Glycogen 47 

Gross anatomy 1 

Habits ' 134 

Haemoglobin 10 

Hair 114 

Haversian canals 95 

Health 1, 169-175 

Hearing 151-156 

Heart 17 

Muscle of 106 

Work of .' 17 

Heat of the body 80 

Heat capacity, impairment of . . 80 

Hepatic vein 72 

Hind-brain 122 

Histology 1 

Hygiene, defined 1 

Of abdomen 56 

Of blood 13 

Of bones 101 

Of circulatory organs 22 

Of digestive organs 22 

Of ear 155 

Of eye 167 

Of excretory organs 90 

Of muscles Ill 

Of nervous system 137 

Of respiratory organs 36 

Of skin 117 

Ileum 64 

Ileo-coecal valve 54, 64 

Images 158 

Insalivation 60 

Intercellular material 3 

Intermediate nerve cells 131 

Intestines 64-67 

Large 67 

Small 64 

Intestinal digestion 65 

Iris 161 

Irritability 104, 128 

Jejunum • 64 

Joints 100, 101 

Kinds of 101 

Structure of 100 

Kidneys 86 

Blood supply of 87 

Structure of . . . .- 87 

Labyrinth 152 

Lachrymal apparatus 166 



Page. 

Lacteals 71 

Lacunae 95 

Large intestine, work of 66 

Larynx 31, 147-150 

Structure of 148 

Levers 109 

Of the body 109 

Light 157 

Lime-water, use of 42 

Preparation of 178 

Liver 65 

Circulation in 66 

Excretory work of 88 

Functions of . 88 

Localization of cerebral functions 135 

Long-sightedness 167 

Lumbar vertebrae 97 

Lungs 30-32 

Dissection of 31 

Excretory work of 89 

Lymph ..." 24-28 

Composition of 24 

Cause of flow of 26 

Movements of 25 

Necessity for 24 

Origin of 24 

Physical properties of 24 

Lymph vessels, lymphatics .... 25 

Lymphatic glands 26 

Maintenance of life 6 

Relation of oxygen to 41 

Marrow, yellow and red 94 

Massage 103 

Mastication 60 

Muscles of 61 

Mechanics of respiration 34 

Medulla 122 

Medullary sheath 125 

Membrana tympani 151 

Membranous labyrinth 152 

Mesentery 55 

Metacarpal bones 98 

Metatarsal bones 98 

Mid-brain 120 

Morphine 139 

Mouth 60 

Accessory organs of 61 

Motion, the problem of 104 

Mucous membrane 58, 113 

Of air passages 32 

Of mouth 60 

Of small intestine 64 

Of stomach 63 

Muscle cells 105 

Muscular tissue 2, 104 

Muscular force 107 

Muscular sensations 144 



18± 



INDEX. 



Page. 

Muscle weakness of the ejes 167 

Nails ' 114 

Nasal duct 166 

Neurilemma 125 

Nerve cells 124 

Function of parts 129 

Properties of 128 

Nerve fibers 125 

Nerve paths 127 

Nerve skeleton 119 

Nerve stimuli 131 

Nerve trunks 119 

Nervous control of circulation . . 135 

Of digestion 137 

Of respiration 136 

Of regulation of temperature. 116 

Nervous impulses 128 

Kinds of 129 

Nature of 128 

Purpose of 129 

Nervous system 119-127 

Functions of 134 

Divisions of 121 

Nervousness 138 

Nervous tissue 1, 119, 128 

Neurone theory 124 

Nicotine 139 

Nitrogen 29 

Non-striated muscle, structure of 106 

Work of 108 

Nucleus 4 

Observations on 

Arteries and veins 18 

Bones 94 

Cells 4 

Circulation in capillaries .... 20 

Heart 15 

Joints 101 

Larynx 150 

Lungs 31 

Pacinian corpuscles 143 

Red corpuscles 9 

Skin 114 

Structure of bone 95 

Structure of muscle 105, 106 

Tissues 2 

Oesophagus 62 

Organ, defined 5 

Osmosis 27 

At the cells 27 

Oxidation 40 

At the cells 41 

Oxygen, passage of 39-44 

From the body 41 

Through the blood 40 



Page. 

Oxygen, preparation of 177 

Properties of 39 

Purpose in the body 40 

Pacinian corpuscles 125 

Pancreatic juice 66 

Pancreas 65 

/Papilla . . . . 114 

Passage of materials through 

body 92 

Patent medicines 13, 68 

Pelvic girdle 97 

Peptones 63 

Pericardium 17 

Peripheral nervous system .... 122 

Perilymph 152, 153 

Periosteum 94 

Perimysium 105 

Peritoneum 55 

Perspiration 88 

Perspiratory glands 88, 113 

Pharynx 31 

Phalanges of fingers and toes . . 98 

Physiology, defined 1 

Pia mater 124 

Plasma 11 

Platelets of the blood 9 

Pleura 34 

Plexus 119 

Pons 122 

Portal circulation 21 

Portal vein 20 

Primitive sheath 125 

Protection of brain and cord . . . 124 

Proteids 47 

Absorption of 71 

Digestion of 63, 66 

Storage of 73 

Proteoses 63 

Protoplasm 4 

Ptyalin 61 

Pulmonary arteries and veins . . 20 

Pulmonary circulation 21 

Pupil . . .' .' 161 

Receptacle of chyle 54, 72 

Reflex action . .' 130-133 

Paths of 131 

Regulation of temperature 45 

Regulation of food supply to cells. 74 

Renal artery and vein 21 

Renal circulation 21 

Reproduction of cells 5 

Respiration 29-37 

Organs of 30 

Purpose of 29 

Retina 161 

Ribs 33, 97 

Right lymphatic duct 25 



INDEX. 



185 



Page. 

Routes to the circulation 72 

Sacrum 9" 

Salivary glands 01 

Salt, common 84 

Salts 48, 71 

Sanitation 171 

Sarcolemma 105 

Sarcoplasm 105 

Sciatic nerve 110 

Scala media 153 

Scala tympani 153 

Scala vestibula 153 

Sclerotic coat 160 

Secretorv process 85 

Self control . . ., 130 

Semi-circular canals 153 

Sensations, production of .... 141-146 

General 141 

Purpose of 141 

Special 141 

Sense organs 142 

Serum albumin 11 

Short-sightedness 167 

Shoulder girdle 07 

Skeleton 03-103 

Plan of 95 

Skin 113-118 

As organ of adaptation 115 

Functions of 115 

Wounds of, treatment 117 

Skull 07 

Sleep 137 

Small intestine 64 

Absorption at 70 

Work of 67 

Smell 145 

Speech 150 

Special senses 141 

Spinal column 00 

Spinal cord 122 

Spinal nerves 123 

Skin 113-118 

Snleen 53, 00 

Sprains 102 

Sound waves 147 

Value of 148 

Starch 47 

Stomach 63 

Stimuli, of muscles 107 

Of nerves 130 

Striated muscles 105 

Storage of nutriment 73 

Stroma, 00 

Sugars 47 

Suspensory ligament 162 

Sweat glands 88 

Sympathetic cells 132 



P A r,K. 

Sympathetic ganglia 123 

System, defined 5 

Svnovial fluid 101 

Synovial membrane 101 

Systemic circulation 20 

Tables of 

Bones 09 

Foods 40, 50 

Passage of food to the cells . . 76 
Passage of waste from the 

cells 89 

Tarsal bones 98 

Taste 144 

Taste buds 144 

Tears 100 

Teeth 01 

Temperature sensations 144 

Tendons 2, 105 

Terminal air spaces 32 

Thoracic duct 25 

Thoracic vertebrae 98 

Tight lacing 50 

Tissues, observation on 2 

Composition of 3 

Kinds of 2 

Nature of 2 

Properties and uses of 3 

Tobacco 22 

Tongue 01 

Touch, sense of 143 

Touch corpuscles 114, 142 

Trachea 31 

Tvmpanum 151 

Urea 85, 88 

Urine 80 

Uriniferous tubes 87 

Valves of veins 19 

Veins, structure of 18 

Important veins 20 

Vena cava, inferior and superior. 20 

Ventilation 37 

Ventricles of heart 10, 17 

Vertebrae 90 

Vestibule 152 

Villi 70 

Vitreous humor 1G2 

Vocation, relation to health 173 

Vocal cords 148 

Voice 150 

Voluntary action 133 

Voluntary muscles 105 

Water, supply of pure 172 

Work in body 24, 48 

Visual inferences 105 

Visual sensations 105 

Work, value of 174 

Yellow spot 101 



22479 SEP 27 1902 



ftPP O T i 



